[PATCH v2 0/3] arm64: Fix invalid si_codes for fault signals

[PATCH v2 0/3] arm64: Fix invalid si_codes for fault signals

[Dave Martin]

Changes since v1:

 * Fixed failing BUILD_BUG_ON() sanity check on NSIGFPE done by x86.
   (Thanks to James Morse for spotting.)

   The addition of FPE_FLTUNK is harmless to x86, since only arm64
   uses this code right now.

Changes since RFC v2:

 * Fold in reverts of the relevant parts of Eric's *_FIXME changes,
   since this series removes all cases of those dummy si_code values
   from arm64.

 * Propagated the new signal/si_code assignments for synchronous
   external aborts correctly to signals thrown from do_sea().

Original blurb:

As reported by Eric Biederman, [1], [2], [3] etc., several architectures
are inappropriately setting si_code to 0 when signaling faults to
userspace, which will interpret this value as SI_USER leading to garbage
being read out of siginfo fields that the kernel doesn't initialise.

This seems not to be a huge problem in practice, since many affected
faults should only happen if the kernel or hardware is buggy or broken.
However, there are some cases that don't fall under this.

This RFC series proposes fixes to eliminate these si_code == 0 cases
from arm64.  Some of the changes may be controversial.

There are two main headlines here, which may be applicable to other
architectures:

 * addition of a new code FPE_UNKNOWN for undiagnosable floating-point
   exception traps;

 * delivering SIGKILL instead of SIGSEGV/BUS/TRAP etc. for "impossible"
   exceptions that are not feasible to recover from and likely indicate
   a kernel or system bug or failure.

In particular there is likely to be a fair amount of overlap between arm
and arm64 here, but due to the longer history and evolution of the arm
tree and 32-bit architecture I'm less confident in making correct
judgements for that case.  This series doesn't touch arm, for now.

Boot-tested on Arm Juno r0.
Floating-point exception traps tested on the Arm Fast Model.

[1] [PATCH 00/11] siginfo fixes/cleanups esp SI_USER
https://marc.info/?l=linux-kernel&m=151571871109016&w=2

[2] [PATCH 08/11] signal/arm: Document conflicts with SI_USER and SIGFPE
http://lists.infradead.org/pipermail/linux-arm-kernel/2018-January/553574.html

[3] [PATCH 07/11] signal/arm64: Document conflicts with SI_USER and SIGFPE, SIGTRAP, SIGBUS
lists.infradead.org/pipermail/linux-arm-kernel/2018-January/553573.html

Dave Martin (3):
  signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions
  arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE
  arm64: signal: Ensure si_code is valid for all fault signals

 arch/arm64/include/asm/esr.h          |   9 +++
 arch/arm64/include/uapi/asm/siginfo.h |  21 ------
 arch/arm64/kernel/fpsimd.c            |  31 +++++----
 arch/arm64/mm/fault.c                 | 116 +++++++++++++++++-----------------
 arch/x86/kernel/signal_compat.c       |   2 +-
 include/uapi/asm-generic/siginfo.h    |   3 +-
 kernel/signal.c                       |   4 --
 7 files changed, 87 insertions(+), 99 deletions(-)

-- 
2.1.4

[PATCH v2 0/3] arm64: Fix invalid si_codes for fault signals

[Dave Martin]

Changes since v1:

 * Fixed failing BUILD_BUG_ON() sanity check on NSIGFPE done by x86.
   (Thanks to James Morse for spotting.)

   The addition of FPE_FLTUNK is harmless to x86, since only arm64
   uses this code right now.

Changes since RFC v2:

 * Fold in reverts of the relevant parts of Eric's *_FIXME changes,
   since this series removes all cases of those dummy si_code values
   from arm64.

 * Propagated the new signal/si_code assignments for synchronous
   external aborts correctly to signals thrown from do_sea().

Original blurb:

As reported by Eric Biederman, [1], [2], [3] etc., several architectures
are inappropriately setting si_code to 0 when signaling faults to
userspace, which will interpret this value as SI_USER leading to garbage
being read out of siginfo fields that the kernel doesn't initialise.

This seems not to be a huge problem in practice, since many affected
faults should only happen if the kernel or hardware is buggy or broken.
However, there are some cases that don't fall under this.

This RFC series proposes fixes to eliminate these si_code == 0 cases
from arm64.  Some of the changes may be controversial.

There are two main headlines here, which may be applicable to other
architectures:

 * addition of a new code FPE_UNKNOWN for undiagnosable floating-point
   exception traps;

 * delivering SIGKILL instead of SIGSEGV/BUS/TRAP etc. for "impossible"
   exceptions that are not feasible to recover from and likely indicate
   a kernel or system bug or failure.

In particular there is likely to be a fair amount of overlap between arm
and arm64 here, but due to the longer history and evolution of the arm
tree and 32-bit architecture I'm less confident in making correct
judgements for that case.  This series doesn't touch arm, for now.

Boot-tested on Arm Juno r0.
Floating-point exception traps tested on the Arm Fast Model.

[1] [PATCH 00/11] siginfo fixes/cleanups esp SI_USER
https://marc.info/?l=linux-kernel&m=151571871109016&w=2

[2] [PATCH 08/11] signal/arm: Document conflicts with SI_USER and SIGFPE
http://lists.infradead.org/pipermail/linux-arm-kernel/2018-January/553574.html

[3] [PATCH 07/11] signal/arm64: Document conflicts with SI_USER and SIGFPE, SIGTRAP, SIGBUS
lists.infradead.org/pipermail/linux-arm-kernel/2018-January/553573.html

Dave Martin (3):
  signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions
  arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE
  arm64: signal: Ensure si_code is valid for all fault signals

 arch/arm64/include/asm/esr.h          |   9 +++
 arch/arm64/include/uapi/asm/siginfo.h |  21 ------
 arch/arm64/kernel/fpsimd.c            |  31 +++++----
 arch/arm64/mm/fault.c                 | 116 +++++++++++++++++-----------------
 arch/x86/kernel/signal_compat.c       |   2 +-
 include/uapi/asm-generic/siginfo.h    |   3 +-
 kernel/signal.c                       |   4 --
 7 files changed, 87 insertions(+), 99 deletions(-)

-- 
2.1.4

[PATCH v2 0/3] arm64: Fix invalid si_codes for fault signals

[Dave Martin]

Changes since v1:

 * Fixed failing BUILD_BUG_ON() sanity check on NSIGFPE done by x86.
   (Thanks to James Morse for spotting.)

   The addition of FPE_FLTUNK is harmless to x86, since only arm64
   uses this code right now.

Changes since RFC v2:

 * Fold in reverts of the relevant parts of Eric's *_FIXME changes,
   since this series removes all cases of those dummy si_code values
   from arm64.

 * Propagated the new signal/si_code assignments for synchronous
   external aborts correctly to signals thrown from do_sea().

Original blurb:

As reported by Eric Biederman, [1], [2], [3] etc., several architectures
are inappropriately setting si_code to 0 when signaling faults to
userspace, which will interpret this value as SI_USER leading to garbage
being read out of siginfo fields that the kernel doesn't initialise.

This seems not to be a huge problem in practice, since many affected
faults should only happen if the kernel or hardware is buggy or broken.
However, there are some cases that don't fall under this.

This RFC series proposes fixes to eliminate these si_code == 0 cases
from arm64.  Some of the changes may be controversial.

There are two main headlines here, which may be applicable to other
architectures:

 * addition of a new code FPE_UNKNOWN for undiagnosable floating-point
   exception traps;

 * delivering SIGKILL instead of SIGSEGV/BUS/TRAP etc. for "impossible"
   exceptions that are not feasible to recover from and likely indicate
   a kernel or system bug or failure.

In particular there is likely to be a fair amount of overlap between arm
and arm64 here, but due to the longer history and evolution of the arm
tree and 32-bit architecture I'm less confident in making correct
judgements for that case.  This series doesn't touch arm, for now.

Boot-tested on Arm Juno r0.
Floating-point exception traps tested on the Arm Fast Model.

[1] [PATCH 00/11] siginfo fixes/cleanups esp SI_USER
https://marc.info/?l=linux-kernel&m=151571871109016&w=2

[2] [PATCH 08/11] signal/arm: Document conflicts with SI_USER and SIGFPE
http://lists.infradead.org/pipermail/linux-arm-kernel/2018-January/553574.html

[3] [PATCH 07/11] signal/arm64: Document conflicts with SI_USER and SIGFPE, SIGTRAP, SIGBUS
lists.infradead.org/pipermail/linux-arm-kernel/2018-January/553573.html

Dave Martin (3):
  signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions
  arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE
  arm64: signal: Ensure si_code is valid for all fault signals

 arch/arm64/include/asm/esr.h          |   9 +++
 arch/arm64/include/uapi/asm/siginfo.h |  21 ------
 arch/arm64/kernel/fpsimd.c            |  31 +++++----
 arch/arm64/mm/fault.c                 | 116 +++++++++++++++++-----------------
 arch/x86/kernel/signal_compat.c       |   2 +-
 include/uapi/asm-generic/siginfo.h    |   3 +-
 kernel/signal.c                       |   4 --
 7 files changed, 87 insertions(+), 99 deletions(-)

-- 
2.1.4

[PATCH v2 1/3] signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

[Dave Martin]

Some architectures cannot always report accurately what kind of
floating-point exception triggered a floating-point exception trap.

This can occur with fp exceptions occurring on lanes in a vector
instruction on arm64 for example.

Rather than have every architecture come up with its own way of
describing such a condition, this patch adds a common FPE_FLTUNK
si_code value to report that an fp exception caused a trap but we
cannot be certain which kind of fp exception it was.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>

--

Changes since v1:

Reported by James Morse:

 * Bump NSIGFPE BUILD_BUG_ON() check for x86 compat.

   FPE_FLTUNK does not current have any implications for x86, since it
   is not currently used and has no implications for the way siginfo
   is populated.
---
 arch/x86/kernel/signal_compat.c    | 2 +-
 include/uapi/asm-generic/siginfo.h | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index ac057f9..954ad99 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c
@@ -26,7 +26,7 @@ static inline void signal_compat_build_tests(void)
 	 * new fields are handled in copy_siginfo_to_user32()!
 	 */
 	BUILD_BUG_ON(NSIGILL  != 11);
-	BUILD_BUG_ON(NSIGFPE  != 13);
+	BUILD_BUG_ON(NSIGFPE  != 14);
 	BUILD_BUG_ON(NSIGSEGV != 4);
 	BUILD_BUG_ON(NSIGBUS  != 5);
 	BUILD_BUG_ON(NSIGTRAP != 4);
diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
index 85dc965..10304de 100644
--- a/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -229,7 +229,8 @@ typedef struct siginfo {
 # define __FPE_INVASC	12	/* invalid ASCII digit */
 # define __FPE_INVDEC	13	/* invalid decimal digit */
 #endif
-#define NSIGFPE		13
+#define FPE_FLTUNK	14	/* undiagnosed floating-point exception */
+#define NSIGFPE		14
 
 /*
  * SIGSEGV si_codes
-- 
2.1.4

[PATCH v2 1/3] signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

[Dave Martin]

Some architectures cannot always report accurately what kind of
floating-point exception triggered a floating-point exception trap.

This can occur with fp exceptions occurring on lanes in a vector
instruction on arm64 for example.

Rather than have every architecture come up with its own way of
describing such a condition, this patch adds a common FPE_FLTUNK
si_code value to report that an fp exception caused a trap but we
cannot be certain which kind of fp exception it was.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>

--

Changes since v1:

Reported by James Morse:

 * Bump NSIGFPE BUILD_BUG_ON() check for x86 compat.

   FPE_FLTUNK does not current have any implications for x86, since it
   is not currently used and has no implications for the way siginfo
   is populated.
---
 arch/x86/kernel/signal_compat.c    | 2 +-
 include/uapi/asm-generic/siginfo.h | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index ac057f9..954ad99 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c
@@ -26,7 +26,7 @@ static inline void signal_compat_build_tests(void)
 	 * new fields are handled in copy_siginfo_to_user32()!
 	 */
 	BUILD_BUG_ON(NSIGILL  != 11);
-	BUILD_BUG_ON(NSIGFPE  != 13);
+	BUILD_BUG_ON(NSIGFPE  != 14);
 	BUILD_BUG_ON(NSIGSEGV != 4);
 	BUILD_BUG_ON(NSIGBUS  != 5);
 	BUILD_BUG_ON(NSIGTRAP != 4);
diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
index 85dc965..10304de 100644
--- a/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -229,7 +229,8 @@ typedef struct siginfo {
 # define __FPE_INVASC	12	/* invalid ASCII digit */
 # define __FPE_INVDEC	13	/* invalid decimal digit */
 #endif
-#define NSIGFPE		13
+#define FPE_FLTUNK	14	/* undiagnosed floating-point exception */
+#define NSIGFPE		14
 
 /*
  * SIGSEGV si_codes
-- 
2.1.4

[PATCH v2 1/3] signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

[Dave Martin]

Some architectures cannot always report accurately what kind of
floating-point exception triggered a floating-point exception trap.

This can occur with fp exceptions occurring on lanes in a vector
instruction on arm64 for example.

Rather than have every architecture come up with its own way of
describing such a condition, this patch adds a common FPE_FLTUNK
si_code value to report that an fp exception caused a trap but we
cannot be certain which kind of fp exception it was.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>

--

Changes since v1:

Reported by James Morse:

 * Bump NSIGFPE BUILD_BUG_ON() check for x86 compat.

   FPE_FLTUNK does not current have any implications for x86, since it
   is not currently used and has no implications for the way siginfo
   is populated.
---
 arch/x86/kernel/signal_compat.c    | 2 +-
 include/uapi/asm-generic/siginfo.h | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index ac057f9..954ad99 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c
@@ -26,7 +26,7 @@ static inline void signal_compat_build_tests(void)
 	 * new fields are handled in copy_siginfo_to_user32()!
 	 */
 	BUILD_BUG_ON(NSIGILL  != 11);
-	BUILD_BUG_ON(NSIGFPE  != 13);
+	BUILD_BUG_ON(NSIGFPE  != 14);
 	BUILD_BUG_ON(NSIGSEGV != 4);
 	BUILD_BUG_ON(NSIGBUS  != 5);
 	BUILD_BUG_ON(NSIGTRAP != 4);
diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
index 85dc965..10304de 100644
--- a/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -229,7 +229,8 @@ typedef struct siginfo {
 # define __FPE_INVASC	12	/* invalid ASCII digit */
 # define __FPE_INVDEC	13	/* invalid decimal digit */
 #endif
-#define NSIGFPE		13
+#define FPE_FLTUNK	14	/* undiagnosed floating-point exception */
+#define NSIGFPE		14
 
 /*
  * SIGSEGV si_codes
-- 
2.1.4

Re: [PATCH v2 1/3] signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

[Will Deacon]

Hi Dave,

On Thu, Mar 01, 2018 at 05:44:06PM +0000, Dave Martin wrote:
> Some architectures cannot always report accurately what kind of
> floating-point exception triggered a floating-point exception trap.
> 
> This can occur with fp exceptions occurring on lanes in a vector
> instruction on arm64 for example.
> 
> Rather than have every architecture come up with its own way of
> describing such a condition, this patch adds a common FPE_FLTUNK
> si_code value to report that an fp exception caused a trap but we
> cannot be certain which kind of fp exception it was.

This looks straightforward to me, but I'll need Acks for the x86 and uapi
changes if I'm to take this via arm64. I've added some others to CC and
kept the patch intact below.

Cheers,

Will

> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> 
> --
> 
> Changes since v1:
> 
> Reported by James Morse:
> 
>  * Bump NSIGFPE BUILD_BUG_ON() check for x86 compat.
> 
>    FPE_FLTUNK does not current have any implications for x86, since it
>    is not currently used and has no implications for the way siginfo
>    is populated.
> ---
>  arch/x86/kernel/signal_compat.c    | 2 +-
>  include/uapi/asm-generic/siginfo.h | 3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
> index ac057f9..954ad99 100644
> --- a/arch/x86/kernel/signal_compat.c
> +++ b/arch/x86/kernel/signal_compat.c
> @@ -26,7 +26,7 @@ static inline void signal_compat_build_tests(void)
>  	 * new fields are handled in copy_siginfo_to_user32()!
>  	 */
>  	BUILD_BUG_ON(NSIGILL  != 11);
> -	BUILD_BUG_ON(NSIGFPE  != 13);
> +	BUILD_BUG_ON(NSIGFPE  != 14);
>  	BUILD_BUG_ON(NSIGSEGV != 4);
>  	BUILD_BUG_ON(NSIGBUS  != 5);
>  	BUILD_BUG_ON(NSIGTRAP != 4);
> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index 85dc965..10304de 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -229,7 +229,8 @@ typedef struct siginfo {
>  # define __FPE_INVASC	12	/* invalid ASCII digit */
>  # define __FPE_INVDEC	13	/* invalid decimal digit */
>  #endif
> -#define NSIGFPE		13
> +#define FPE_FLTUNK	14	/* undiagnosed floating-point exception */
> +#define NSIGFPE		14
>  
>  /*
>   * SIGSEGV si_codes
> -- 
> 2.1.4
> 

[PATCH v2 1/3] signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

[Will Deacon]

Hi Dave,

On Thu, Mar 01, 2018 at 05:44:06PM +0000, Dave Martin wrote:
> Some architectures cannot always report accurately what kind of
> floating-point exception triggered a floating-point exception trap.
> 
> This can occur with fp exceptions occurring on lanes in a vector
> instruction on arm64 for example.
> 
> Rather than have every architecture come up with its own way of
> describing such a condition, this patch adds a common FPE_FLTUNK
> si_code value to report that an fp exception caused a trap but we
> cannot be certain which kind of fp exception it was.

This looks straightforward to me, but I'll need Acks for the x86 and uapi
changes if I'm to take this via arm64. I've added some others to CC and
kept the patch intact below.

Cheers,

Will

> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> 
> --
> 
> Changes since v1:
> 
> Reported by James Morse:
> 
>  * Bump NSIGFPE BUILD_BUG_ON() check for x86 compat.
> 
>    FPE_FLTUNK does not current have any implications for x86, since it
>    is not currently used and has no implications for the way siginfo
>    is populated.
> ---
>  arch/x86/kernel/signal_compat.c    | 2 +-
>  include/uapi/asm-generic/siginfo.h | 3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
> index ac057f9..954ad99 100644
> --- a/arch/x86/kernel/signal_compat.c
> +++ b/arch/x86/kernel/signal_compat.c
> @@ -26,7 +26,7 @@ static inline void signal_compat_build_tests(void)
>  	 * new fields are handled in copy_siginfo_to_user32()!
>  	 */
>  	BUILD_BUG_ON(NSIGILL  != 11);
> -	BUILD_BUG_ON(NSIGFPE  != 13);
> +	BUILD_BUG_ON(NSIGFPE  != 14);
>  	BUILD_BUG_ON(NSIGSEGV != 4);
>  	BUILD_BUG_ON(NSIGBUS  != 5);
>  	BUILD_BUG_ON(NSIGTRAP != 4);
> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index 85dc965..10304de 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -229,7 +229,8 @@ typedef struct siginfo {
>  # define __FPE_INVASC	12	/* invalid ASCII digit */
>  # define __FPE_INVDEC	13	/* invalid decimal digit */
>  #endif
> -#define NSIGFPE		13
> +#define FPE_FLTUNK	14	/* undiagnosed floating-point exception */
> +#define NSIGFPE		14
>  
>  /*
>   * SIGSEGV si_codes
> -- 
> 2.1.4
> 

Re: [PATCH v2 1/3] signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

[Eric W. Biederman]

Dave Martin <Dave.Martin@arm.com> writes:

> Some architectures cannot always report accurately what kind of
> floating-point exception triggered a floating-point exception trap.
>
> This can occur with fp exceptions occurring on lanes in a vector
> instruction on arm64 for example.
>
> Rather than have every architecture come up with its own way of
> describing such a condition, this patch adds a common FPE_FLTUNK
> si_code value to report that an fp exception caused a trap but we
> cannot be certain which kind of fp exception it was.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>

> --
>
> Changes since v1:
>
> Reported by James Morse:
>
>  * Bump NSIGFPE BUILD_BUG_ON() check for x86 compat.
>
>    FPE_FLTUNK does not current have any implications for x86, since it
>    is not currently used and has no implications for the way siginfo
>    is populated.
> ---
>  arch/x86/kernel/signal_compat.c    | 2 +-
>  include/uapi/asm-generic/siginfo.h | 3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
> index ac057f9..954ad99 100644
> --- a/arch/x86/kernel/signal_compat.c
> +++ b/arch/x86/kernel/signal_compat.c
> @@ -26,7 +26,7 @@ static inline void signal_compat_build_tests(void)
>  	 * new fields are handled in copy_siginfo_to_user32()!
>  	 */
>  	BUILD_BUG_ON(NSIGILL  != 11);
> -	BUILD_BUG_ON(NSIGFPE  != 13);
> +	BUILD_BUG_ON(NSIGFPE  != 14);
>  	BUILD_BUG_ON(NSIGSEGV != 4);
>  	BUILD_BUG_ON(NSIGBUS  != 5);
>  	BUILD_BUG_ON(NSIGTRAP != 4);

For other reviewers.  This bug on exists to ensure people remember to
update the helper functions when new fields are added to struct siginfo.
As new fields usually come with new si_codes.  There are no fields
added so this is sufficient.

> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index 85dc965..10304de 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -229,7 +229,8 @@ typedef struct siginfo {
>  # define __FPE_INVASC	12	/* invalid ASCII digit */
>  # define __FPE_INVDEC	13	/* invalid decimal digit */
>  #endif
> -#define NSIGFPE		13
> +#define FPE_FLTUNK	14	/* undiagnosed floating-point exception */
> +#define NSIGFPE		14
>  
>  /*
>   * SIGSEGV si_codes

[PATCH v2 1/3] signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

[Eric W. Biederman]

Dave Martin <Dave.Martin@arm.com> writes:

> Some architectures cannot always report accurately what kind of
> floating-point exception triggered a floating-point exception trap.
>
> This can occur with fp exceptions occurring on lanes in a vector
> instruction on arm64 for example.
>
> Rather than have every architecture come up with its own way of
> describing such a condition, this patch adds a common FPE_FLTUNK
> si_code value to report that an fp exception caused a trap but we
> cannot be certain which kind of fp exception it was.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>

> --
>
> Changes since v1:
>
> Reported by James Morse:
>
>  * Bump NSIGFPE BUILD_BUG_ON() check for x86 compat.
>
>    FPE_FLTUNK does not current have any implications for x86, since it
>    is not currently used and has no implications for the way siginfo
>    is populated.
> ---
>  arch/x86/kernel/signal_compat.c    | 2 +-
>  include/uapi/asm-generic/siginfo.h | 3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
> index ac057f9..954ad99 100644
> --- a/arch/x86/kernel/signal_compat.c
> +++ b/arch/x86/kernel/signal_compat.c
> @@ -26,7 +26,7 @@ static inline void signal_compat_build_tests(void)
>  	 * new fields are handled in copy_siginfo_to_user32()!
>  	 */
>  	BUILD_BUG_ON(NSIGILL  != 11);
> -	BUILD_BUG_ON(NSIGFPE  != 13);
> +	BUILD_BUG_ON(NSIGFPE  != 14);
>  	BUILD_BUG_ON(NSIGSEGV != 4);
>  	BUILD_BUG_ON(NSIGBUS  != 5);
>  	BUILD_BUG_ON(NSIGTRAP != 4);

For other reviewers.  This bug on exists to ensure people remember to
update the helper functions when new fields are added to struct siginfo.
As new fields usually come with new si_codes.  There are no fields
added so this is sufficient.

> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index 85dc965..10304de 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -229,7 +229,8 @@ typedef struct siginfo {
>  # define __FPE_INVASC	12	/* invalid ASCII digit */
>  # define __FPE_INVDEC	13	/* invalid decimal digit */
>  #endif
> -#define NSIGFPE		13
> +#define FPE_FLTUNK	14	/* undiagnosed floating-point exception */
> +#define NSIGFPE		14
>  
>  /*
>   * SIGSEGV si_codes

Re: [PATCH v2 1/3] signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

[Eric W. Biederman]

Dave Martin <Dave.Martin@arm.com> writes:

> Some architectures cannot always report accurately what kind of
> floating-point exception triggered a floating-point exception trap.
>
> This can occur with fp exceptions occurring on lanes in a vector
> instruction on arm64 for example.
>
> Rather than have every architecture come up with its own way of
> describing such a condition, this patch adds a common FPE_FLTUNK
> si_code value to report that an fp exception caused a trap but we
> cannot be certain which kind of fp exception it was.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>

> --
>
> Changes since v1:
>
> Reported by James Morse:
>
>  * Bump NSIGFPE BUILD_BUG_ON() check for x86 compat.
>
>    FPE_FLTUNK does not current have any implications for x86, since it
>    is not currently used and has no implications for the way siginfo
>    is populated.
> ---
>  arch/x86/kernel/signal_compat.c    | 2 +-
>  include/uapi/asm-generic/siginfo.h | 3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
> index ac057f9..954ad99 100644
> --- a/arch/x86/kernel/signal_compat.c
> +++ b/arch/x86/kernel/signal_compat.c
> @@ -26,7 +26,7 @@ static inline void signal_compat_build_tests(void)
>  	 * new fields are handled in copy_siginfo_to_user32()!
>  	 */
>  	BUILD_BUG_ON(NSIGILL  != 11);
> -	BUILD_BUG_ON(NSIGFPE  != 13);
> +	BUILD_BUG_ON(NSIGFPE  != 14);
>  	BUILD_BUG_ON(NSIGSEGV != 4);
>  	BUILD_BUG_ON(NSIGBUS  != 5);
>  	BUILD_BUG_ON(NSIGTRAP != 4);

For other reviewers.  This bug on exists to ensure people remember to
update the helper functions when new fields are added to struct siginfo.
As new fields usually come with new si_codes.  There are no fields
added so this is sufficient.

> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index 85dc965..10304de 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -229,7 +229,8 @@ typedef struct siginfo {
>  # define __FPE_INVASC	12	/* invalid ASCII digit */
>  # define __FPE_INVDEC	13	/* invalid decimal digit */
>  #endif
> -#define NSIGFPE		13
> +#define FPE_FLTUNK	14	/* undiagnosed floating-point exception */
> +#define NSIGFPE		14
>  
>  /*
>   * SIGSEGV si_codes

[PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Dave Martin]

Currently a SIGFPE delivered in response to a floating-point
exception trap may have si_code set to 0 on arm64.  As reported by
Eric, this is a bad idea since this is the value of SI_USER -- yet
this signal is definitely not the result of kill(2), tgkill(2) etc.
and si_uid and si_pid make limited sense whereas we do want to
yield a value for si_addr (which doesn't exist for SI_USER).

It's not entirely clear whether the architecure permits a
"spurious" fp exception trap where none of the exception flag bits
in ESR_ELx is set.  (IMHO the architectural intent is to forbid
this.)  However, it does permit those bits to contain garbage if
the TFV bit in ESR_ELx is 0.  That case isn't currently handled at
all and may result in si_code == 0 or si_code containing a FPE_FLT*
constant corresponding to an exception that did not in fact happen.

There is nothing sensible we can return for si_code in such cases,
but SI_USER is certainly not appropriate and will lead to violation
of legitimate userspace assumptions.

This patch allocates a new si_code value FPE_UNKNOWN that at least
does not conflict with any existing SI_* or FPE_* code, and yields
this in si_code for undiagnosable cases.  This is probably the best
simplicity/incorrectness tradeoff achieveable without relying on
implementation-dependent features or adding a lot of code.  In any
case, there appears to be no perfect solution possible that would
justify a lot of effort here.

Yielding FPE_UNKNOWN when some well-defined fp exception caused the
trap is a violation of POSIX, but this is forced by the
architecture.  We have no realistic prospect of yielding the
correct code in such cases.  At present I am not aware of any ARMv8
implementation that supports trapped floating-point exceptions in
any case.

The new code may be applicable to other architectures for similar
reasons.

No attempt is made to provide ESR_ELx to userspace in the signal
frame, since architectural limitations mean that it is unlikely to
provide much diagnostic value, doesn't benefit existing software
and would create ABI with no proven purpose.  The existing
mechanism for passing it also has problems of its own which may
result in the wrong value being passed to userspace due to
interaction with mm faults.  The implied rework does not appear
justified.

Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
 arch/arm64/include/asm/esr.h          |  9 +++++++++
 arch/arm64/include/uapi/asm/siginfo.h |  7 -------
 arch/arm64/kernel/fpsimd.c            | 27 +++++++++++++++------------
 3 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index 803443d..ce70c3f 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -240,6 +240,15 @@
 		(((e) & ESR_ELx_SYS64_ISS_OP2_MASK) >>		\
 		 ESR_ELx_SYS64_ISS_OP2_SHIFT))
 
+/*
+ * ISS field definitions for floating-point exception traps
+ * (FP_EXC_32/FP_EXC_64).
+ *
+ * (The FPEXC_* constants are used instead for common bits.)
+ */
+
+#define ESR_ELx_FP_EXC_TFV	(UL(1) << 23)
+
 #ifndef __ASSEMBLY__
 #include <asm/types.h>
 
diff --git a/arch/arm64/include/uapi/asm/siginfo.h b/arch/arm64/include/uapi/asm/siginfo.h
index 9b4d912..157e6a8 100644
--- a/arch/arm64/include/uapi/asm/siginfo.h
+++ b/arch/arm64/include/uapi/asm/siginfo.h
@@ -22,13 +22,6 @@
 #include <asm-generic/siginfo.h>
 
 /*
- * SIGFPE si_codes
- */
-#ifdef __KERNEL__
-#define FPE_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
-/*
  * SIGBUS si_codes
  */
 #ifdef __KERNEL__
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index e7226c4..9040038 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -39,6 +39,7 @@
 #include <linux/slab.h>
 #include <linux/sysctl.h>
 
+#include <asm/esr.h>
 #include <asm/fpsimd.h>
 #include <asm/cputype.h>
 #include <asm/simd.h>
@@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
 asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
 {
 	siginfo_t info;
-	unsigned int si_code = FPE_FIXME;
-
-	if (esr & FPEXC_IOF)
-		si_code = FPE_FLTINV;
-	else if (esr & FPEXC_DZF)
-		si_code = FPE_FLTDIV;
-	else if (esr & FPEXC_OFF)
-		si_code = FPE_FLTOVF;
-	else if (esr & FPEXC_UFF)
-		si_code = FPE_FLTUND;
-	else if (esr & FPEXC_IXF)
-		si_code = FPE_FLTRES;
+	unsigned int si_code = FPE_FLTUNK;
+
+	if (esr & ESR_ELx_FP_EXC_TFV) {
+		if (esr & FPEXC_IOF)
+			si_code = FPE_FLTINV;
+		else if (esr & FPEXC_DZF)
+			si_code = FPE_FLTDIV;
+		else if (esr & FPEXC_OFF)
+			si_code = FPE_FLTOVF;
+		else if (esr & FPEXC_UFF)
+			si_code = FPE_FLTUND;
+		else if (esr & FPEXC_IXF)
+			si_code = FPE_FLTRES;
+	}
 
 	memset(&info, 0, sizeof(info));
 	info.si_signo = SIGFPE;
-- 
2.1.4

[PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Dave Martin]

Currently a SIGFPE delivered in response to a floating-point
exception trap may have si_code set to 0 on arm64.  As reported by
Eric, this is a bad idea since this is the value of SI_USER -- yet
this signal is definitely not the result of kill(2), tgkill(2) etc.
and si_uid and si_pid make limited sense whereas we do want to
yield a value for si_addr (which doesn't exist for SI_USER).

It's not entirely clear whether the architecure permits a
"spurious" fp exception trap where none of the exception flag bits
in ESR_ELx is set.  (IMHO the architectural intent is to forbid
this.)  However, it does permit those bits to contain garbage if
the TFV bit in ESR_ELx is 0.  That case isn't currently handled at
all and may result in si_code == 0 or si_code containing a FPE_FLT*
constant corresponding to an exception that did not in fact happen.

There is nothing sensible we can return for si_code in such cases,
but SI_USER is certainly not appropriate and will lead to violation
of legitimate userspace assumptions.

This patch allocates a new si_code value FPE_UNKNOWN that at least
does not conflict with any existing SI_* or FPE_* code, and yields
this in si_code for undiagnosable cases.  This is probably the best
simplicity/incorrectness tradeoff achieveable without relying on
implementation-dependent features or adding a lot of code.  In any
case, there appears to be no perfect solution possible that would
justify a lot of effort here.

Yielding FPE_UNKNOWN when some well-defined fp exception caused the
trap is a violation of POSIX, but this is forced by the
architecture.  We have no realistic prospect of yielding the
correct code in such cases.  At present I am not aware of any ARMv8
implementation that supports trapped floating-point exceptions in
any case.

The new code may be applicable to other architectures for similar
reasons.

No attempt is made to provide ESR_ELx to userspace in the signal
frame, since architectural limitations mean that it is unlikely to
provide much diagnostic value, doesn't benefit existing software
and would create ABI with no proven purpose.  The existing
mechanism for passing it also has problems of its own which may
result in the wrong value being passed to userspace due to
interaction with mm faults.  The implied rework does not appear
justified.

Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
 arch/arm64/include/asm/esr.h          |  9 +++++++++
 arch/arm64/include/uapi/asm/siginfo.h |  7 -------
 arch/arm64/kernel/fpsimd.c            | 27 +++++++++++++++------------
 3 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index 803443d..ce70c3f 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -240,6 +240,15 @@
 		(((e) & ESR_ELx_SYS64_ISS_OP2_MASK) >>		\
 		 ESR_ELx_SYS64_ISS_OP2_SHIFT))
 
+/*
+ * ISS field definitions for floating-point exception traps
+ * (FP_EXC_32/FP_EXC_64).
+ *
+ * (The FPEXC_* constants are used instead for common bits.)
+ */
+
+#define ESR_ELx_FP_EXC_TFV	(UL(1) << 23)
+
 #ifndef __ASSEMBLY__
 #include <asm/types.h>
 
diff --git a/arch/arm64/include/uapi/asm/siginfo.h b/arch/arm64/include/uapi/asm/siginfo.h
index 9b4d912..157e6a8 100644
--- a/arch/arm64/include/uapi/asm/siginfo.h
+++ b/arch/arm64/include/uapi/asm/siginfo.h
@@ -22,13 +22,6 @@
 #include <asm-generic/siginfo.h>
 
 /*
- * SIGFPE si_codes
- */
-#ifdef __KERNEL__
-#define FPE_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
-/*
  * SIGBUS si_codes
  */
 #ifdef __KERNEL__
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index e7226c4..9040038 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -39,6 +39,7 @@
 #include <linux/slab.h>
 #include <linux/sysctl.h>
 
+#include <asm/esr.h>
 #include <asm/fpsimd.h>
 #include <asm/cputype.h>
 #include <asm/simd.h>
@@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
 asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
 {
 	siginfo_t info;
-	unsigned int si_code = FPE_FIXME;
-
-	if (esr & FPEXC_IOF)
-		si_code = FPE_FLTINV;
-	else if (esr & FPEXC_DZF)
-		si_code = FPE_FLTDIV;
-	else if (esr & FPEXC_OFF)
-		si_code = FPE_FLTOVF;
-	else if (esr & FPEXC_UFF)
-		si_code = FPE_FLTUND;
-	else if (esr & FPEXC_IXF)
-		si_code = FPE_FLTRES;
+	unsigned int si_code = FPE_FLTUNK;
+
+	if (esr & ESR_ELx_FP_EXC_TFV) {
+		if (esr & FPEXC_IOF)
+			si_code = FPE_FLTINV;
+		else if (esr & FPEXC_DZF)
+			si_code = FPE_FLTDIV;
+		else if (esr & FPEXC_OFF)
+			si_code = FPE_FLTOVF;
+		else if (esr & FPEXC_UFF)
+			si_code = FPE_FLTUND;
+		else if (esr & FPEXC_IXF)
+			si_code = FPE_FLTRES;
+	}
 
 	memset(&info, 0, sizeof(info));
 	info.si_signo = SIGFPE;
-- 
2.1.4

[PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Dave Martin]

Currently a SIGFPE delivered in response to a floating-point
exception trap may have si_code set to 0 on arm64.  As reported by
Eric, this is a bad idea since this is the value of SI_USER -- yet
this signal is definitely not the result of kill(2), tgkill(2) etc.
and si_uid and si_pid make limited sense whereas we do want to
yield a value for si_addr (which doesn't exist for SI_USER).

It's not entirely clear whether the architecure permits a
"spurious" fp exception trap where none of the exception flag bits
in ESR_ELx is set.  (IMHO the architectural intent is to forbid
this.)  However, it does permit those bits to contain garbage if
the TFV bit in ESR_ELx is 0.  That case isn't currently handled at
all and may result in si_code == 0 or si_code containing a FPE_FLT*
constant corresponding to an exception that did not in fact happen.

There is nothing sensible we can return for si_code in such cases,
but SI_USER is certainly not appropriate and will lead to violation
of legitimate userspace assumptions.

This patch allocates a new si_code value FPE_UNKNOWN that at least
does not conflict with any existing SI_* or FPE_* code, and yields
this in si_code for undiagnosable cases.  This is probably the best
simplicity/incorrectness tradeoff achieveable without relying on
implementation-dependent features or adding a lot of code.  In any
case, there appears to be no perfect solution possible that would
justify a lot of effort here.

Yielding FPE_UNKNOWN when some well-defined fp exception caused the
trap is a violation of POSIX, but this is forced by the
architecture.  We have no realistic prospect of yielding the
correct code in such cases.  At present I am not aware of any ARMv8
implementation that supports trapped floating-point exceptions in
any case.

The new code may be applicable to other architectures for similar
reasons.

No attempt is made to provide ESR_ELx to userspace in the signal
frame, since architectural limitations mean that it is unlikely to
provide much diagnostic value, doesn't benefit existing software
and would create ABI with no proven purpose.  The existing
mechanism for passing it also has problems of its own which may
result in the wrong value being passed to userspace due to
interaction with mm faults.  The implied rework does not appear
justified.

Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
 arch/arm64/include/asm/esr.h          |  9 +++++++++
 arch/arm64/include/uapi/asm/siginfo.h |  7 -------
 arch/arm64/kernel/fpsimd.c            | 27 +++++++++++++++------------
 3 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index 803443d..ce70c3f 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -240,6 +240,15 @@
 		(((e) & ESR_ELx_SYS64_ISS_OP2_MASK) >>		\
 		 ESR_ELx_SYS64_ISS_OP2_SHIFT))
 
+/*
+ * ISS field definitions for floating-point exception traps
+ * (FP_EXC_32/FP_EXC_64).
+ *
+ * (The FPEXC_* constants are used instead for common bits.)
+ */
+
+#define ESR_ELx_FP_EXC_TFV	(UL(1) << 23)
+
 #ifndef __ASSEMBLY__
 #include <asm/types.h>
 
diff --git a/arch/arm64/include/uapi/asm/siginfo.h b/arch/arm64/include/uapi/asm/siginfo.h
index 9b4d912..157e6a8 100644
--- a/arch/arm64/include/uapi/asm/siginfo.h
+++ b/arch/arm64/include/uapi/asm/siginfo.h
@@ -22,13 +22,6 @@
 #include <asm-generic/siginfo.h>
 
 /*
- * SIGFPE si_codes
- */
-#ifdef __KERNEL__
-#define FPE_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
-/*
  * SIGBUS si_codes
  */
 #ifdef __KERNEL__
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index e7226c4..9040038 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -39,6 +39,7 @@
 #include <linux/slab.h>
 #include <linux/sysctl.h>
 
+#include <asm/esr.h>
 #include <asm/fpsimd.h>
 #include <asm/cputype.h>
 #include <asm/simd.h>
@@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
 asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
 {
 	siginfo_t info;
-	unsigned int si_code = FPE_FIXME;
-
-	if (esr & FPEXC_IOF)
-		si_code = FPE_FLTINV;
-	else if (esr & FPEXC_DZF)
-		si_code = FPE_FLTDIV;
-	else if (esr & FPEXC_OFF)
-		si_code = FPE_FLTOVF;
-	else if (esr & FPEXC_UFF)
-		si_code = FPE_FLTUND;
-	else if (esr & FPEXC_IXF)
-		si_code = FPE_FLTRES;
+	unsigned int si_code = FPE_FLTUNK;
+
+	if (esr & ESR_ELx_FP_EXC_TFV) {
+		if (esr & FPEXC_IOF)
+			si_code = FPE_FLTINV;
+		else if (esr & FPEXC_DZF)
+			si_code = FPE_FLTDIV;
+		else if (esr & FPEXC_OFF)
+			si_code = FPE_FLTOVF;
+		else if (esr & FPEXC_UFF)
+			si_code = FPE_FLTUND;
+		else if (esr & FPEXC_IXF)
+			si_code = FPE_FLTRES;
+	}
 
 	memset(&info, 0, sizeof(info));
 	info.si_signo = SIGFPE;
-- 
2.1.4

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Will Deacon]

On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
> Currently a SIGFPE delivered in response to a floating-point
> exception trap may have si_code set to 0 on arm64.  As reported by
> Eric, this is a bad idea since this is the value of SI_USER -- yet
> this signal is definitely not the result of kill(2), tgkill(2) etc.
> and si_uid and si_pid make limited sense whereas we do want to
> yield a value for si_addr (which doesn't exist for SI_USER).

[...]

> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index e7226c4..9040038 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -39,6 +39,7 @@
>  #include <linux/slab.h>
>  #include <linux/sysctl.h>
>  
> +#include <asm/esr.h>
>  #include <asm/fpsimd.h>
>  #include <asm/cputype.h>
>  #include <asm/simd.h>
> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
>  {
>  	siginfo_t info;
> -	unsigned int si_code = FPE_FIXME;
> -
> -	if (esr & FPEXC_IOF)
> -		si_code = FPE_FLTINV;
> -	else if (esr & FPEXC_DZF)
> -		si_code = FPE_FLTDIV;
> -	else if (esr & FPEXC_OFF)
> -		si_code = FPE_FLTOVF;
> -	else if (esr & FPEXC_UFF)
> -		si_code = FPE_FLTUND;
> -	else if (esr & FPEXC_IXF)
> -		si_code = FPE_FLTRES;
> +	unsigned int si_code = FPE_FLTUNK;

Happy to take this patch once the dependency on FPE_FLTUNK in core code is
resolved.

Will

[PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Will Deacon]

On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
> Currently a SIGFPE delivered in response to a floating-point
> exception trap may have si_code set to 0 on arm64.  As reported by
> Eric, this is a bad idea since this is the value of SI_USER -- yet
> this signal is definitely not the result of kill(2), tgkill(2) etc.
> and si_uid and si_pid make limited sense whereas we do want to
> yield a value for si_addr (which doesn't exist for SI_USER).

[...]

> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index e7226c4..9040038 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -39,6 +39,7 @@
>  #include <linux/slab.h>
>  #include <linux/sysctl.h>
>  
> +#include <asm/esr.h>
>  #include <asm/fpsimd.h>
>  #include <asm/cputype.h>
>  #include <asm/simd.h>
> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
>  {
>  	siginfo_t info;
> -	unsigned int si_code = FPE_FIXME;
> -
> -	if (esr & FPEXC_IOF)
> -		si_code = FPE_FLTINV;
> -	else if (esr & FPEXC_DZF)
> -		si_code = FPE_FLTDIV;
> -	else if (esr & FPEXC_OFF)
> -		si_code = FPE_FLTOVF;
> -	else if (esr & FPEXC_UFF)
> -		si_code = FPE_FLTUND;
> -	else if (esr & FPEXC_IXF)
> -		si_code = FPE_FLTRES;
> +	unsigned int si_code = FPE_FLTUNK;

Happy to take this patch once the dependency on FPE_FLTUNK in core code is
resolved.

Will

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Will Deacon]

On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
> Currently a SIGFPE delivered in response to a floating-point
> exception trap may have si_code set to 0 on arm64.  As reported by
> Eric, this is a bad idea since this is the value of SI_USER -- yet
> this signal is definitely not the result of kill(2), tgkill(2) etc.
> and si_uid and si_pid make limited sense whereas we do want to
> yield a value for si_addr (which doesn't exist for SI_USER).

[...]

> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index e7226c4..9040038 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -39,6 +39,7 @@
>  #include <linux/slab.h>
>  #include <linux/sysctl.h>
>  
> +#include <asm/esr.h>
>  #include <asm/fpsimd.h>
>  #include <asm/cputype.h>
>  #include <asm/simd.h>
> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
>  {
>  	siginfo_t info;
> -	unsigned int si_code = FPE_FIXME;
> -
> -	if (esr & FPEXC_IOF)
> -		si_code = FPE_FLTINV;
> -	else if (esr & FPEXC_DZF)
> -		si_code = FPE_FLTDIV;
> -	else if (esr & FPEXC_OFF)
> -		si_code = FPE_FLTOVF;
> -	else if (esr & FPEXC_UFF)
> -		si_code = FPE_FLTUND;
> -	else if (esr & FPEXC_IXF)
> -		si_code = FPE_FLTRES;
> +	unsigned int si_code = FPE_FLTUNK;

Happy to take this patch once the dependency on FPE_FLTUNK in core code is
resolved.

Will

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Eric W. Biederman]

Will Deacon <will.deacon@arm.com> writes:

> On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
>> Currently a SIGFPE delivered in response to a floating-point
>> exception trap may have si_code set to 0 on arm64.  As reported by
>> Eric, this is a bad idea since this is the value of SI_USER -- yet
>> this signal is definitely not the result of kill(2), tgkill(2) etc.
>> and si_uid and si_pid make limited sense whereas we do want to
>> yield a value for si_addr (which doesn't exist for SI_USER).
>
> [...]
>
>> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
>> index e7226c4..9040038 100644
>> --- a/arch/arm64/kernel/fpsimd.c
>> +++ b/arch/arm64/kernel/fpsimd.c
>> @@ -39,6 +39,7 @@
>>  #include <linux/slab.h>
>>  #include <linux/sysctl.h>
>>  
>> +#include <asm/esr.h>
>>  #include <asm/fpsimd.h>
>>  #include <asm/cputype.h>
>>  #include <asm/simd.h>
>> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
>>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
>>  {
>>  	siginfo_t info;
>> -	unsigned int si_code = FPE_FIXME;
>> -
>> -	if (esr & FPEXC_IOF)
>> -		si_code = FPE_FLTINV;
>> -	else if (esr & FPEXC_DZF)
>> -		si_code = FPE_FLTDIV;
>> -	else if (esr & FPEXC_OFF)
>> -		si_code = FPE_FLTOVF;
>> -	else if (esr & FPEXC_UFF)
>> -		si_code = FPE_FLTUND;
>> -	else if (esr & FPEXC_IXF)
>> -		si_code = FPE_FLTRES;
>> +	unsigned int si_code = FPE_FLTUNK;
>
> Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> resolved.

Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
branch?   So that there is a common branch with the code so we don't
need to worry about conflicts.  If so I will look at that on Monday.

There is another FPE code that appears to be needed for one of the other
architectures as well.  If we can figure out how to head conflicts off
at the pass while everyone is fixing the FPE_FIXME type problems it
might help.

But it is all simple enough I expect a word to the wise when I send
Linus my pull request will be enough to sort things out.

Eric

[PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Eric W. Biederman]

Will Deacon <will.deacon@arm.com> writes:

> On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
>> Currently a SIGFPE delivered in response to a floating-point
>> exception trap may have si_code set to 0 on arm64.  As reported by
>> Eric, this is a bad idea since this is the value of SI_USER -- yet
>> this signal is definitely not the result of kill(2), tgkill(2) etc.
>> and si_uid and si_pid make limited sense whereas we do want to
>> yield a value for si_addr (which doesn't exist for SI_USER).
>
> [...]
>
>> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
>> index e7226c4..9040038 100644
>> --- a/arch/arm64/kernel/fpsimd.c
>> +++ b/arch/arm64/kernel/fpsimd.c
>> @@ -39,6 +39,7 @@
>>  #include <linux/slab.h>
>>  #include <linux/sysctl.h>
>>  
>> +#include <asm/esr.h>
>>  #include <asm/fpsimd.h>
>>  #include <asm/cputype.h>
>>  #include <asm/simd.h>
>> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
>>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
>>  {
>>  	siginfo_t info;
>> -	unsigned int si_code = FPE_FIXME;
>> -
>> -	if (esr & FPEXC_IOF)
>> -		si_code = FPE_FLTINV;
>> -	else if (esr & FPEXC_DZF)
>> -		si_code = FPE_FLTDIV;
>> -	else if (esr & FPEXC_OFF)
>> -		si_code = FPE_FLTOVF;
>> -	else if (esr & FPEXC_UFF)
>> -		si_code = FPE_FLTUND;
>> -	else if (esr & FPEXC_IXF)
>> -		si_code = FPE_FLTRES;
>> +	unsigned int si_code = FPE_FLTUNK;
>
> Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> resolved.

Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
branch?   So that there is a common branch with the code so we don't
need to worry about conflicts.  If so I will look at that on Monday.

There is another FPE code that appears to be needed for one of the other
architectures as well.  If we can figure out how to head conflicts off
at the pass while everyone is fixing the FPE_FIXME type problems it
might help.

But it is all simple enough I expect a word to the wise when I send
Linus my pull request will be enough to sort things out.

Eric

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Eric W. Biederman]

Will Deacon <will.deacon@arm.com> writes:

> On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
>> Currently a SIGFPE delivered in response to a floating-point
>> exception trap may have si_code set to 0 on arm64.  As reported by
>> Eric, this is a bad idea since this is the value of SI_USER -- yet
>> this signal is definitely not the result of kill(2), tgkill(2) etc.
>> and si_uid and si_pid make limited sense whereas we do want to
>> yield a value for si_addr (which doesn't exist for SI_USER).
>
> [...]
>
>> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
>> index e7226c4..9040038 100644
>> --- a/arch/arm64/kernel/fpsimd.c
>> +++ b/arch/arm64/kernel/fpsimd.c
>> @@ -39,6 +39,7 @@
>>  #include <linux/slab.h>
>>  #include <linux/sysctl.h>
>>  
>> +#include <asm/esr.h>
>>  #include <asm/fpsimd.h>
>>  #include <asm/cputype.h>
>>  #include <asm/simd.h>
>> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
>>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
>>  {
>>  	siginfo_t info;
>> -	unsigned int si_code = FPE_FIXME;
>> -
>> -	if (esr & FPEXC_IOF)
>> -		si_code = FPE_FLTINV;
>> -	else if (esr & FPEXC_DZF)
>> -		si_code = FPE_FLTDIV;
>> -	else if (esr & FPEXC_OFF)
>> -		si_code = FPE_FLTOVF;
>> -	else if (esr & FPEXC_UFF)
>> -		si_code = FPE_FLTUND;
>> -	else if (esr & FPEXC_IXF)
>> -		si_code = FPE_FLTRES;
>> +	unsigned int si_code = FPE_FLTUNK;
>
> Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> resolved.

Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
branch?   So that there is a common branch with the code so we don't
need to worry about conflicts.  If so I will look at that on Monday.

There is another FPE code that appears to be needed for one of the other
architectures as well.  If we can figure out how to head conflicts off
at the pass while everyone is fixing the FPE_FIXME type problems it
might help.

But it is all simple enough I expect a word to the wise when I send
Linus my pull request will be enough to sort things out.

Eric

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Will Deacon]

Hi Eric,

On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
> Will Deacon <will.deacon@arm.com> writes:
> 
> > On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
> >> Currently a SIGFPE delivered in response to a floating-point
> >> exception trap may have si_code set to 0 on arm64.  As reported by
> >> Eric, this is a bad idea since this is the value of SI_USER -- yet
> >> this signal is definitely not the result of kill(2), tgkill(2) etc.
> >> and si_uid and si_pid make limited sense whereas we do want to
> >> yield a value for si_addr (which doesn't exist for SI_USER).
> >
> > [...]
> >
> >> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> >> index e7226c4..9040038 100644
> >> --- a/arch/arm64/kernel/fpsimd.c
> >> +++ b/arch/arm64/kernel/fpsimd.c
> >> @@ -39,6 +39,7 @@
> >>  #include <linux/slab.h>
> >>  #include <linux/sysctl.h>
> >>  
> >> +#include <asm/esr.h>
> >>  #include <asm/fpsimd.h>
> >>  #include <asm/cputype.h>
> >>  #include <asm/simd.h>
> >> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
> >>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
> >>  {
> >>  	siginfo_t info;
> >> -	unsigned int si_code = FPE_FIXME;
> >> -
> >> -	if (esr & FPEXC_IOF)
> >> -		si_code = FPE_FLTINV;
> >> -	else if (esr & FPEXC_DZF)
> >> -		si_code = FPE_FLTDIV;
> >> -	else if (esr & FPEXC_OFF)
> >> -		si_code = FPE_FLTOVF;
> >> -	else if (esr & FPEXC_UFF)
> >> -		si_code = FPE_FLTUND;
> >> -	else if (esr & FPEXC_IXF)
> >> -		si_code = FPE_FLTRES;
> >> +	unsigned int si_code = FPE_FLTUNK;
> >
> > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> > resolved.
> 
> Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
> branch?   So that there is a common branch with the code so we don't
> need to worry about conflicts.  If so I will look at that on Monday.

Yes please, that would be helpful actually. I can then pull that into
arm64 if you give me a stable branch or tag. Alternatively, I can define
FPE_FLTUNK locally and remove it at -rc1.

Cheers,

Will

[PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Will Deacon]

Hi Eric,

On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
> Will Deacon <will.deacon@arm.com> writes:
> 
> > On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
> >> Currently a SIGFPE delivered in response to a floating-point
> >> exception trap may have si_code set to 0 on arm64.  As reported by
> >> Eric, this is a bad idea since this is the value of SI_USER -- yet
> >> this signal is definitely not the result of kill(2), tgkill(2) etc.
> >> and si_uid and si_pid make limited sense whereas we do want to
> >> yield a value for si_addr (which doesn't exist for SI_USER).
> >
> > [...]
> >
> >> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> >> index e7226c4..9040038 100644
> >> --- a/arch/arm64/kernel/fpsimd.c
> >> +++ b/arch/arm64/kernel/fpsimd.c
> >> @@ -39,6 +39,7 @@
> >>  #include <linux/slab.h>
> >>  #include <linux/sysctl.h>
> >>  
> >> +#include <asm/esr.h>
> >>  #include <asm/fpsimd.h>
> >>  #include <asm/cputype.h>
> >>  #include <asm/simd.h>
> >> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
> >>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
> >>  {
> >>  	siginfo_t info;
> >> -	unsigned int si_code = FPE_FIXME;
> >> -
> >> -	if (esr & FPEXC_IOF)
> >> -		si_code = FPE_FLTINV;
> >> -	else if (esr & FPEXC_DZF)
> >> -		si_code = FPE_FLTDIV;
> >> -	else if (esr & FPEXC_OFF)
> >> -		si_code = FPE_FLTOVF;
> >> -	else if (esr & FPEXC_UFF)
> >> -		si_code = FPE_FLTUND;
> >> -	else if (esr & FPEXC_IXF)
> >> -		si_code = FPE_FLTRES;
> >> +	unsigned int si_code = FPE_FLTUNK;
> >
> > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> > resolved.
> 
> Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
> branch?   So that there is a common branch with the code so we don't
> need to worry about conflicts.  If so I will look at that on Monday.

Yes please, that would be helpful actually. I can then pull that into
arm64 if you give me a stable branch or tag. Alternatively, I can define
FPE_FLTUNK locally and remove it at -rc1.

Cheers,

Will

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Will Deacon]

Hi Eric,

On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
> Will Deacon <will.deacon@arm.com> writes:
> 
> > On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
> >> Currently a SIGFPE delivered in response to a floating-point
> >> exception trap may have si_code set to 0 on arm64.  As reported by
> >> Eric, this is a bad idea since this is the value of SI_USER -- yet
> >> this signal is definitely not the result of kill(2), tgkill(2) etc.
> >> and si_uid and si_pid make limited sense whereas we do want to
> >> yield a value for si_addr (which doesn't exist for SI_USER).
> >
> > [...]
> >
> >> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> >> index e7226c4..9040038 100644
> >> --- a/arch/arm64/kernel/fpsimd.c
> >> +++ b/arch/arm64/kernel/fpsimd.c
> >> @@ -39,6 +39,7 @@
> >>  #include <linux/slab.h>
> >>  #include <linux/sysctl.h>
> >>  
> >> +#include <asm/esr.h>
> >>  #include <asm/fpsimd.h>
> >>  #include <asm/cputype.h>
> >>  #include <asm/simd.h>
> >> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
> >>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
> >>  {
> >>  	siginfo_t info;
> >> -	unsigned int si_code = FPE_FIXME;
> >> -
> >> -	if (esr & FPEXC_IOF)
> >> -		si_code = FPE_FLTINV;
> >> -	else if (esr & FPEXC_DZF)
> >> -		si_code = FPE_FLTDIV;
> >> -	else if (esr & FPEXC_OFF)
> >> -		si_code = FPE_FLTOVF;
> >> -	else if (esr & FPEXC_UFF)
> >> -		si_code = FPE_FLTUND;
> >> -	else if (esr & FPEXC_IXF)
> >> -		si_code = FPE_FLTRES;
> >> +	unsigned int si_code = FPE_FLTUNK;
> >
> > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> > resolved.
> 
> Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
> branch?   So that there is a common branch with the code so we don't
> need to worry about conflicts.  If so I will look at that on Monday.

Yes please, that would be helpful actually. I can then pull that into
arm64 if you give me a stable branch or tag. Alternatively, I can define
FPE_FLTUNK locally and remove it at -rc1.

Cheers,

Will

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Dave Martin]

On Fri, Mar 09, 2018 at 01:10:18PM +0000, Will Deacon wrote:
> Hi Eric,
> 
> On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
> > Will Deacon <will.deacon@arm.com> writes:
> > 
> > > On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
> > >> Currently a SIGFPE delivered in response to a floating-point
> > >> exception trap may have si_code set to 0 on arm64.  As reported by
> > >> Eric, this is a bad idea since this is the value of SI_USER -- yet
> > >> this signal is definitely not the result of kill(2), tgkill(2) etc.
> > >> and si_uid and si_pid make limited sense whereas we do want to
> > >> yield a value for si_addr (which doesn't exist for SI_USER).
> > >
> > > [...]
> > >
> > >> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> > >> index e7226c4..9040038 100644
> > >> --- a/arch/arm64/kernel/fpsimd.c
> > >> +++ b/arch/arm64/kernel/fpsimd.c
> > >> @@ -39,6 +39,7 @@
> > >>  #include <linux/slab.h>
> > >>  #include <linux/sysctl.h>
> > >>  
> > >> +#include <asm/esr.h>
> > >>  #include <asm/fpsimd.h>
> > >>  #include <asm/cputype.h>
> > >>  #include <asm/simd.h>
> > >> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
> > >>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
> > >>  {
> > >>  	siginfo_t info;
> > >> -	unsigned int si_code = FPE_FIXME;
> > >> -
> > >> -	if (esr & FPEXC_IOF)
> > >> -		si_code = FPE_FLTINV;
> > >> -	else if (esr & FPEXC_DZF)
> > >> -		si_code = FPE_FLTDIV;
> > >> -	else if (esr & FPEXC_OFF)
> > >> -		si_code = FPE_FLTOVF;
> > >> -	else if (esr & FPEXC_UFF)
> > >> -		si_code = FPE_FLTUND;
> > >> -	else if (esr & FPEXC_IXF)
> > >> -		si_code = FPE_FLTRES;
> > >> +	unsigned int si_code = FPE_FLTUNK;
> > >
> > > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> > > resolved.
> > 
> > Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
> > branch?   So that there is a common branch with the code so we don't
> > need to worry about conflicts.  If so I will look at that on Monday.
> 
> Yes please, that would be helpful actually. I can then pull that into
> arm64 if you give me a stable branch or tag. Alternatively, I can define
> FPE_FLTUNK locally and remove it at -rc1.

OK Eric, let me know if you need me to rebase anything for the first 2
patches.

Cheers
---Dave

[PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Dave Martin]

On Fri, Mar 09, 2018 at 01:10:18PM +0000, Will Deacon wrote:
> Hi Eric,
> 
> On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
> > Will Deacon <will.deacon@arm.com> writes:
> > 
> > > On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
> > >> Currently a SIGFPE delivered in response to a floating-point
> > >> exception trap may have si_code set to 0 on arm64.  As reported by
> > >> Eric, this is a bad idea since this is the value of SI_USER -- yet
> > >> this signal is definitely not the result of kill(2), tgkill(2) etc.
> > >> and si_uid and si_pid make limited sense whereas we do want to
> > >> yield a value for si_addr (which doesn't exist for SI_USER).
> > >
> > > [...]
> > >
> > >> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> > >> index e7226c4..9040038 100644
> > >> --- a/arch/arm64/kernel/fpsimd.c
> > >> +++ b/arch/arm64/kernel/fpsimd.c
> > >> @@ -39,6 +39,7 @@
> > >>  #include <linux/slab.h>
> > >>  #include <linux/sysctl.h>
> > >>  
> > >> +#include <asm/esr.h>
> > >>  #include <asm/fpsimd.h>
> > >>  #include <asm/cputype.h>
> > >>  #include <asm/simd.h>
> > >> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
> > >>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
> > >>  {
> > >>  	siginfo_t info;
> > >> -	unsigned int si_code = FPE_FIXME;
> > >> -
> > >> -	if (esr & FPEXC_IOF)
> > >> -		si_code = FPE_FLTINV;
> > >> -	else if (esr & FPEXC_DZF)
> > >> -		si_code = FPE_FLTDIV;
> > >> -	else if (esr & FPEXC_OFF)
> > >> -		si_code = FPE_FLTOVF;
> > >> -	else if (esr & FPEXC_UFF)
> > >> -		si_code = FPE_FLTUND;
> > >> -	else if (esr & FPEXC_IXF)
> > >> -		si_code = FPE_FLTRES;
> > >> +	unsigned int si_code = FPE_FLTUNK;
> > >
> > > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> > > resolved.
> > 
> > Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
> > branch?   So that there is a common branch with the code so we don't
> > need to worry about conflicts.  If so I will look at that on Monday.
> 
> Yes please, that would be helpful actually. I can then pull that into
> arm64 if you give me a stable branch or tag. Alternatively, I can define
> FPE_FLTUNK locally and remove it at -rc1.

OK Eric, let me know if you need me to rebase anything for the first 2
patches.

Cheers
---Dave

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Dave Martin]

On Fri, Mar 09, 2018 at 01:10:18PM +0000, Will Deacon wrote:
> Hi Eric,
> 
> On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
> > Will Deacon <will.deacon@arm.com> writes:
> > 
> > > On Thu, Mar 01, 2018 at 05:44:07PM +0000, Dave Martin wrote:
> > >> Currently a SIGFPE delivered in response to a floating-point
> > >> exception trap may have si_code set to 0 on arm64.  As reported by
> > >> Eric, this is a bad idea since this is the value of SI_USER -- yet
> > >> this signal is definitely not the result of kill(2), tgkill(2) etc.
> > >> and si_uid and si_pid make limited sense whereas we do want to
> > >> yield a value for si_addr (which doesn't exist for SI_USER).
> > >
> > > [...]
> > >
> > >> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> > >> index e7226c4..9040038 100644
> > >> --- a/arch/arm64/kernel/fpsimd.c
> > >> +++ b/arch/arm64/kernel/fpsimd.c
> > >> @@ -39,6 +39,7 @@
> > >>  #include <linux/slab.h>
> > >>  #include <linux/sysctl.h>
> > >>  
> > >> +#include <asm/esr.h>
> > >>  #include <asm/fpsimd.h>
> > >>  #include <asm/cputype.h>
> > >>  #include <asm/simd.h>
> > >> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
> > >>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
> > >>  {
> > >>  	siginfo_t info;
> > >> -	unsigned int si_code = FPE_FIXME;
> > >> -
> > >> -	if (esr & FPEXC_IOF)
> > >> -		si_code = FPE_FLTINV;
> > >> -	else if (esr & FPEXC_DZF)
> > >> -		si_code = FPE_FLTDIV;
> > >> -	else if (esr & FPEXC_OFF)
> > >> -		si_code = FPE_FLTOVF;
> > >> -	else if (esr & FPEXC_UFF)
> > >> -		si_code = FPE_FLTUND;
> > >> -	else if (esr & FPEXC_IXF)
> > >> -		si_code = FPE_FLTRES;
> > >> +	unsigned int si_code = FPE_FLTUNK;
> > >
> > > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> > > resolved.
> > 
> > Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
> > branch?   So that there is a common branch with the code so we don't
> > need to worry about conflicts.  If so I will look at that on Monday.
> 
> Yes please, that would be helpful actually. I can then pull that into
> arm64 if you give me a stable branch or tag. Alternatively, I can define
> FPE_FLTUNK locally and remove it at -rc1.

OK Eric, let me know if you need me to rebase anything for the first 2
patches.

Cheers
---Dave

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Eric W. Biederman]

Dave Martin <Dave.Martin@arm.com> writes:

> On Fri, Mar 09, 2018 at 01:10:18PM +0000, Will Deacon wrote:
>> Hi Eric,
>> 
>> On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
>> > Will Deacon <will.deacon@arm.com> writes:
>> > > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
>> > > resolved.
>> > 
>> > Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
>> > branch?   So that there is a common branch with the code so we don't
>> > need to worry about conflicts.  If so I will look at that on Monday.
>> 
>> Yes please, that would be helpful actually. I can then pull that into
>> arm64 if you give me a stable branch or tag. Alternatively, I can define
>> FPE_FLTUNK locally and remove it at -rc1.
>
> OK Eric, let me know if you need me to rebase anything for the first 2
> patches.

The first patch is now in my siginfo-next tree and avialable at:

git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git siginfo-next
HEAD: 266da65e9156d93e1126e185259a4aae68188d0e signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

I will not rebase this branch, so please fee free to merge it into other
trees.

Eric

[PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Eric W. Biederman]

Dave Martin <Dave.Martin@arm.com> writes:

> On Fri, Mar 09, 2018 at 01:10:18PM +0000, Will Deacon wrote:
>> Hi Eric,
>> 
>> On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
>> > Will Deacon <will.deacon@arm.com> writes:
>> > > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
>> > > resolved.
>> > 
>> > Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
>> > branch?   So that there is a common branch with the code so we don't
>> > need to worry about conflicts.  If so I will look at that on Monday.
>> 
>> Yes please, that would be helpful actually. I can then pull that into
>> arm64 if you give me a stable branch or tag. Alternatively, I can define
>> FPE_FLTUNK locally and remove it at -rc1.
>
> OK Eric, let me know if you need me to rebase anything for the first 2
> patches.

The first patch is now in my siginfo-next tree and avialable at:

git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git siginfo-next
HEAD: 266da65e9156d93e1126e185259a4aae68188d0e signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

I will not rebase this branch, so please fee free to merge it into other
trees.

Eric

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Eric W. Biederman]

Dave Martin <Dave.Martin@arm.com> writes:

> On Fri, Mar 09, 2018 at 01:10:18PM +0000, Will Deacon wrote:
>> Hi Eric,
>> 
>> On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
>> > Will Deacon <will.deacon@arm.com> writes:
>> > > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
>> > > resolved.
>> > 
>> > Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
>> > branch?   So that there is a common branch with the code so we don't
>> > need to worry about conflicts.  If so I will look at that on Monday.
>> 
>> Yes please, that would be helpful actually. I can then pull that into
>> arm64 if you give me a stable branch or tag. Alternatively, I can define
>> FPE_FLTUNK locally and remove it at -rc1.
>
> OK Eric, let me know if you need me to rebase anything for the first 2
> patches.

The first patch is now in my siginfo-next tree and avialable at:

git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git siginfo-next
HEAD: 266da65e9156d93e1126e185259a4aae68188d0e signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions

I will not rebase this branch, so please fee free to merge it into other
trees.

Eric

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Will Deacon]

On Thu, Mar 15, 2018 at 04:13:02PM -0500, Eric W. Biederman wrote:
> Dave Martin <Dave.Martin@arm.com> writes:
> 
> > On Fri, Mar 09, 2018 at 01:10:18PM +0000, Will Deacon wrote:
> >> Hi Eric,
> >> 
> >> On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
> >> > Will Deacon <will.deacon@arm.com> writes:
> >> > > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> >> > > resolved.
> >> > 
> >> > Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
> >> > branch?   So that there is a common branch with the code so we don't
> >> > need to worry about conflicts.  If so I will look at that on Monday.
> >> 
> >> Yes please, that would be helpful actually. I can then pull that into
> >> arm64 if you give me a stable branch or tag. Alternatively, I can define
> >> FPE_FLTUNK locally and remove it at -rc1.
> >
> > OK Eric, let me know if you need me to rebase anything for the first 2
> > patches.
> 
> The first patch is now in my siginfo-next tree and avialable at:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git siginfo-next
> HEAD: 266da65e9156d93e1126e185259a4aae68188d0e signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions
> 
> I will not rebase this branch, so please fee free to merge it into other
> trees.

Thanks, Eric. I've pulled this into the arm64 for-next/core branch and I'll
push it out later on.

Will

[PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Will Deacon]

On Thu, Mar 15, 2018 at 04:13:02PM -0500, Eric W. Biederman wrote:
> Dave Martin <Dave.Martin@arm.com> writes:
> 
> > On Fri, Mar 09, 2018 at 01:10:18PM +0000, Will Deacon wrote:
> >> Hi Eric,
> >> 
> >> On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
> >> > Will Deacon <will.deacon@arm.com> writes:
> >> > > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> >> > > resolved.
> >> > 
> >> > Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
> >> > branch?   So that there is a common branch with the code so we don't
> >> > need to worry about conflicts.  If so I will look at that on Monday.
> >> 
> >> Yes please, that would be helpful actually. I can then pull that into
> >> arm64 if you give me a stable branch or tag. Alternatively, I can define
> >> FPE_FLTUNK locally and remove it at -rc1.
> >
> > OK Eric, let me know if you need me to rebase anything for the first 2
> > patches.
> 
> The first patch is now in my siginfo-next tree and avialable at:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git siginfo-next
> HEAD: 266da65e9156d93e1126e185259a4aae68188d0e signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions
> 
> I will not rebase this branch, so please fee free to merge it into other
> trees.

Thanks, Eric. I've pulled this into the arm64 for-next/core branch and I'll
push it out later on.

Will

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Will Deacon]

On Thu, Mar 15, 2018 at 04:13:02PM -0500, Eric W. Biederman wrote:
> Dave Martin <Dave.Martin@arm.com> writes:
> 
> > On Fri, Mar 09, 2018 at 01:10:18PM +0000, Will Deacon wrote:
> >> Hi Eric,
> >> 
> >> On Thu, Mar 08, 2018 at 04:40:12PM -0600, Eric W. Biederman wrote:
> >> > Will Deacon <will.deacon@arm.com> writes:
> >> > > Happy to take this patch once the dependency on FPE_FLTUNK in core code is
> >> > > resolved.
> >> > 
> >> > Would it help for me to take the FPE_FLTUNK patch into my siginfo-next
> >> > branch?   So that there is a common branch with the code so we don't
> >> > need to worry about conflicts.  If so I will look at that on Monday.
> >> 
> >> Yes please, that would be helpful actually. I can then pull that into
> >> arm64 if you give me a stable branch or tag. Alternatively, I can define
> >> FPE_FLTUNK locally and remove it at -rc1.
> >
> > OK Eric, let me know if you need me to rebase anything for the first 2
> > patches.
> 
> The first patch is now in my siginfo-next tree and avialable at:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git siginfo-next
> HEAD: 266da65e9156d93e1126e185259a4aae68188d0e signal: Add FPE_FLTUNK si_code for undiagnosable fp exceptions
> 
> I will not rebase this branch, so please fee free to merge it into other
> trees.

Thanks, Eric. I've pulled this into the arm64 for-next/core branch and I'll
push it out later on.

Will

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Eric W. Biederman]

Dave Martin <Dave.Martin@arm.com> writes:

> Currently a SIGFPE delivered in response to a floating-point
> exception trap may have si_code set to 0 on arm64.  As reported by
> Eric, this is a bad idea since this is the value of SI_USER -- yet
> this signal is definitely not the result of kill(2), tgkill(2) etc.
> and si_uid and si_pid make limited sense whereas we do want to
> yield a value for si_addr (which doesn't exist for SI_USER).
>
> It's not entirely clear whether the architecure permits a
> "spurious" fp exception trap where none of the exception flag bits
> in ESR_ELx is set.  (IMHO the architectural intent is to forbid
> this.)  However, it does permit those bits to contain garbage if
> the TFV bit in ESR_ELx is 0.  That case isn't currently handled at
> all and may result in si_code == 0 or si_code containing a FPE_FLT*
> constant corresponding to an exception that did not in fact happen.
>
> There is nothing sensible we can return for si_code in such cases,
> but SI_USER is certainly not appropriate and will lead to violation
> of legitimate userspace assumptions.
>
> This patch allocates a new si_code value FPE_UNKNOWN that at least
> does not conflict with any existing SI_* or FPE_* code, and yields
> this in si_code for undiagnosable cases.  This is probably the best
> simplicity/incorrectness tradeoff achieveable without relying on
> implementation-dependent features or adding a lot of code.  In any
> case, there appears to be no perfect solution possible that would
> justify a lot of effort here.
>
> Yielding FPE_UNKNOWN when some well-defined fp exception caused the
> trap is a violation of POSIX, but this is forced by the
> architecture.  We have no realistic prospect of yielding the
> correct code in such cases.  At present I am not aware of any ARMv8
> implementation that supports trapped floating-point exceptions in
> any case.
>
> The new code may be applicable to other architectures for similar
> reasons.
>
> No attempt is made to provide ESR_ELx to userspace in the signal
> frame, since architectural limitations mean that it is unlikely to
> provide much diagnostic value, doesn't benefit existing software
> and would create ABI with no proven purpose.  The existing
> mechanism for passing it also has problems of its own which may
> result in the wrong value being passed to userspace due to
> interaction with mm faults.  The implied rework does not appear
> justified.
>
> Reported-by: Eric W. Biederman <ebiederm@xmission.com>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>

> ---
>  arch/arm64/include/asm/esr.h          |  9 +++++++++
>  arch/arm64/include/uapi/asm/siginfo.h |  7 -------
>  arch/arm64/kernel/fpsimd.c            | 27 +++++++++++++++------------
>  3 files changed, 24 insertions(+), 19 deletions(-)
>
> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> index 803443d..ce70c3f 100644
> --- a/arch/arm64/include/asm/esr.h
> +++ b/arch/arm64/include/asm/esr.h
> @@ -240,6 +240,15 @@
>  		(((e) & ESR_ELx_SYS64_ISS_OP2_MASK) >>		\
>  		 ESR_ELx_SYS64_ISS_OP2_SHIFT))
>  
> +/*
> + * ISS field definitions for floating-point exception traps
> + * (FP_EXC_32/FP_EXC_64).
> + *
> + * (The FPEXC_* constants are used instead for common bits.)
> + */
> +
> +#define ESR_ELx_FP_EXC_TFV	(UL(1) << 23)
> +
>  #ifndef __ASSEMBLY__
>  #include <asm/types.h>
>  
> diff --git a/arch/arm64/include/uapi/asm/siginfo.h b/arch/arm64/include/uapi/asm/siginfo.h
> index 9b4d912..157e6a8 100644
> --- a/arch/arm64/include/uapi/asm/siginfo.h
> +++ b/arch/arm64/include/uapi/asm/siginfo.h
> @@ -22,13 +22,6 @@
>  #include <asm-generic/siginfo.h>
>  
>  /*
> - * SIGFPE si_codes
> - */
> -#ifdef __KERNEL__
> -#define FPE_FIXME	0	/* Broken dup of SI_USER */
> -#endif /* __KERNEL__ */
> -
> -/*
>   * SIGBUS si_codes
>   */
>  #ifdef __KERNEL__
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index e7226c4..9040038 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -39,6 +39,7 @@
>  #include <linux/slab.h>
>  #include <linux/sysctl.h>
>  
> +#include <asm/esr.h>
>  #include <asm/fpsimd.h>
>  #include <asm/cputype.h>
>  #include <asm/simd.h>
> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
>  {
>  	siginfo_t info;
> -	unsigned int si_code = FPE_FIXME;
> -
> -	if (esr & FPEXC_IOF)
> -		si_code = FPE_FLTINV;
> -	else if (esr & FPEXC_DZF)
> -		si_code = FPE_FLTDIV;
> -	else if (esr & FPEXC_OFF)
> -		si_code = FPE_FLTOVF;
> -	else if (esr & FPEXC_UFF)
> -		si_code = FPE_FLTUND;
> -	else if (esr & FPEXC_IXF)
> -		si_code = FPE_FLTRES;
> +	unsigned int si_code = FPE_FLTUNK;
> +
> +	if (esr & ESR_ELx_FP_EXC_TFV) {
> +		if (esr & FPEXC_IOF)
> +			si_code = FPE_FLTINV;
> +		else if (esr & FPEXC_DZF)
> +			si_code = FPE_FLTDIV;
> +		else if (esr & FPEXC_OFF)
> +			si_code = FPE_FLTOVF;
> +		else if (esr & FPEXC_UFF)
> +			si_code = FPE_FLTUND;
> +		else if (esr & FPEXC_IXF)
> +			si_code = FPE_FLTRES;
> +	}
>  
>  	memset(&info, 0, sizeof(info));
>  	info.si_signo = SIGFPE;

[PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Eric W. Biederman]

Dave Martin <Dave.Martin@arm.com> writes:

> Currently a SIGFPE delivered in response to a floating-point
> exception trap may have si_code set to 0 on arm64.  As reported by
> Eric, this is a bad idea since this is the value of SI_USER -- yet
> this signal is definitely not the result of kill(2), tgkill(2) etc.
> and si_uid and si_pid make limited sense whereas we do want to
> yield a value for si_addr (which doesn't exist for SI_USER).
>
> It's not entirely clear whether the architecure permits a
> "spurious" fp exception trap where none of the exception flag bits
> in ESR_ELx is set.  (IMHO the architectural intent is to forbid
> this.)  However, it does permit those bits to contain garbage if
> the TFV bit in ESR_ELx is 0.  That case isn't currently handled at
> all and may result in si_code == 0 or si_code containing a FPE_FLT*
> constant corresponding to an exception that did not in fact happen.
>
> There is nothing sensible we can return for si_code in such cases,
> but SI_USER is certainly not appropriate and will lead to violation
> of legitimate userspace assumptions.
>
> This patch allocates a new si_code value FPE_UNKNOWN that at least
> does not conflict with any existing SI_* or FPE_* code, and yields
> this in si_code for undiagnosable cases.  This is probably the best
> simplicity/incorrectness tradeoff achieveable without relying on
> implementation-dependent features or adding a lot of code.  In any
> case, there appears to be no perfect solution possible that would
> justify a lot of effort here.
>
> Yielding FPE_UNKNOWN when some well-defined fp exception caused the
> trap is a violation of POSIX, but this is forced by the
> architecture.  We have no realistic prospect of yielding the
> correct code in such cases.  At present I am not aware of any ARMv8
> implementation that supports trapped floating-point exceptions in
> any case.
>
> The new code may be applicable to other architectures for similar
> reasons.
>
> No attempt is made to provide ESR_ELx to userspace in the signal
> frame, since architectural limitations mean that it is unlikely to
> provide much diagnostic value, doesn't benefit existing software
> and would create ABI with no proven purpose.  The existing
> mechanism for passing it also has problems of its own which may
> result in the wrong value being passed to userspace due to
> interaction with mm faults.  The implied rework does not appear
> justified.
>
> Reported-by: Eric W. Biederman <ebiederm@xmission.com>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>

> ---
>  arch/arm64/include/asm/esr.h          |  9 +++++++++
>  arch/arm64/include/uapi/asm/siginfo.h |  7 -------
>  arch/arm64/kernel/fpsimd.c            | 27 +++++++++++++++------------
>  3 files changed, 24 insertions(+), 19 deletions(-)
>
> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> index 803443d..ce70c3f 100644
> --- a/arch/arm64/include/asm/esr.h
> +++ b/arch/arm64/include/asm/esr.h
> @@ -240,6 +240,15 @@
>  		(((e) & ESR_ELx_SYS64_ISS_OP2_MASK) >>		\
>  		 ESR_ELx_SYS64_ISS_OP2_SHIFT))
>  
> +/*
> + * ISS field definitions for floating-point exception traps
> + * (FP_EXC_32/FP_EXC_64).
> + *
> + * (The FPEXC_* constants are used instead for common bits.)
> + */
> +
> +#define ESR_ELx_FP_EXC_TFV	(UL(1) << 23)
> +
>  #ifndef __ASSEMBLY__
>  #include <asm/types.h>
>  
> diff --git a/arch/arm64/include/uapi/asm/siginfo.h b/arch/arm64/include/uapi/asm/siginfo.h
> index 9b4d912..157e6a8 100644
> --- a/arch/arm64/include/uapi/asm/siginfo.h
> +++ b/arch/arm64/include/uapi/asm/siginfo.h
> @@ -22,13 +22,6 @@
>  #include <asm-generic/siginfo.h>
>  
>  /*
> - * SIGFPE si_codes
> - */
> -#ifdef __KERNEL__
> -#define FPE_FIXME	0	/* Broken dup of SI_USER */
> -#endif /* __KERNEL__ */
> -
> -/*
>   * SIGBUS si_codes
>   */
>  #ifdef __KERNEL__
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index e7226c4..9040038 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -39,6 +39,7 @@
>  #include <linux/slab.h>
>  #include <linux/sysctl.h>
>  
> +#include <asm/esr.h>
>  #include <asm/fpsimd.h>
>  #include <asm/cputype.h>
>  #include <asm/simd.h>
> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
>  {
>  	siginfo_t info;
> -	unsigned int si_code = FPE_FIXME;
> -
> -	if (esr & FPEXC_IOF)
> -		si_code = FPE_FLTINV;
> -	else if (esr & FPEXC_DZF)
> -		si_code = FPE_FLTDIV;
> -	else if (esr & FPEXC_OFF)
> -		si_code = FPE_FLTOVF;
> -	else if (esr & FPEXC_UFF)
> -		si_code = FPE_FLTUND;
> -	else if (esr & FPEXC_IXF)
> -		si_code = FPE_FLTRES;
> +	unsigned int si_code = FPE_FLTUNK;
> +
> +	if (esr & ESR_ELx_FP_EXC_TFV) {
> +		if (esr & FPEXC_IOF)
> +			si_code = FPE_FLTINV;
> +		else if (esr & FPEXC_DZF)
> +			si_code = FPE_FLTDIV;
> +		else if (esr & FPEXC_OFF)
> +			si_code = FPE_FLTOVF;
> +		else if (esr & FPEXC_UFF)
> +			si_code = FPE_FLTUND;
> +		else if (esr & FPEXC_IXF)
> +			si_code = FPE_FLTRES;
> +	}
>  
>  	memset(&info, 0, sizeof(info));
>  	info.si_signo = SIGFPE;

Re: [PATCH v2 2/3] arm64: fpsimd: Fix bad si_code for undiagnosed SIGFPE

[Eric W. Biederman]

Dave Martin <Dave.Martin@arm.com> writes:

> Currently a SIGFPE delivered in response to a floating-point
> exception trap may have si_code set to 0 on arm64.  As reported by
> Eric, this is a bad idea since this is the value of SI_USER -- yet
> this signal is definitely not the result of kill(2), tgkill(2) etc.
> and si_uid and si_pid make limited sense whereas we do want to
> yield a value for si_addr (which doesn't exist for SI_USER).
>
> It's not entirely clear whether the architecure permits a
> "spurious" fp exception trap where none of the exception flag bits
> in ESR_ELx is set.  (IMHO the architectural intent is to forbid
> this.)  However, it does permit those bits to contain garbage if
> the TFV bit in ESR_ELx is 0.  That case isn't currently handled at
> all and may result in si_code == 0 or si_code containing a FPE_FLT*
> constant corresponding to an exception that did not in fact happen.
>
> There is nothing sensible we can return for si_code in such cases,
> but SI_USER is certainly not appropriate and will lead to violation
> of legitimate userspace assumptions.
>
> This patch allocates a new si_code value FPE_UNKNOWN that at least
> does not conflict with any existing SI_* or FPE_* code, and yields
> this in si_code for undiagnosable cases.  This is probably the best
> simplicity/incorrectness tradeoff achieveable without relying on
> implementation-dependent features or adding a lot of code.  In any
> case, there appears to be no perfect solution possible that would
> justify a lot of effort here.
>
> Yielding FPE_UNKNOWN when some well-defined fp exception caused the
> trap is a violation of POSIX, but this is forced by the
> architecture.  We have no realistic prospect of yielding the
> correct code in such cases.  At present I am not aware of any ARMv8
> implementation that supports trapped floating-point exceptions in
> any case.
>
> The new code may be applicable to other architectures for similar
> reasons.
>
> No attempt is made to provide ESR_ELx to userspace in the signal
> frame, since architectural limitations mean that it is unlikely to
> provide much diagnostic value, doesn't benefit existing software
> and would create ABI with no proven purpose.  The existing
> mechanism for passing it also has problems of its own which may
> result in the wrong value being passed to userspace due to
> interaction with mm faults.  The implied rework does not appear
> justified.
>
> Reported-by: Eric W. Biederman <ebiederm@xmission.com>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>

> ---
>  arch/arm64/include/asm/esr.h          |  9 +++++++++
>  arch/arm64/include/uapi/asm/siginfo.h |  7 -------
>  arch/arm64/kernel/fpsimd.c            | 27 +++++++++++++++------------
>  3 files changed, 24 insertions(+), 19 deletions(-)
>
> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> index 803443d..ce70c3f 100644
> --- a/arch/arm64/include/asm/esr.h
> +++ b/arch/arm64/include/asm/esr.h
> @@ -240,6 +240,15 @@
>  		(((e) & ESR_ELx_SYS64_ISS_OP2_MASK) >>		\
>  		 ESR_ELx_SYS64_ISS_OP2_SHIFT))
>  
> +/*
> + * ISS field definitions for floating-point exception traps
> + * (FP_EXC_32/FP_EXC_64).
> + *
> + * (The FPEXC_* constants are used instead for common bits.)
> + */
> +
> +#define ESR_ELx_FP_EXC_TFV	(UL(1) << 23)
> +
>  #ifndef __ASSEMBLY__
>  #include <asm/types.h>
>  
> diff --git a/arch/arm64/include/uapi/asm/siginfo.h b/arch/arm64/include/uapi/asm/siginfo.h
> index 9b4d912..157e6a8 100644
> --- a/arch/arm64/include/uapi/asm/siginfo.h
> +++ b/arch/arm64/include/uapi/asm/siginfo.h
> @@ -22,13 +22,6 @@
>  #include <asm-generic/siginfo.h>
>  
>  /*
> - * SIGFPE si_codes
> - */
> -#ifdef __KERNEL__
> -#define FPE_FIXME	0	/* Broken dup of SI_USER */
> -#endif /* __KERNEL__ */
> -
> -/*
>   * SIGBUS si_codes
>   */
>  #ifdef __KERNEL__
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index e7226c4..9040038 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -39,6 +39,7 @@
>  #include <linux/slab.h>
>  #include <linux/sysctl.h>
>  
> +#include <asm/esr.h>
>  #include <asm/fpsimd.h>
>  #include <asm/cputype.h>
>  #include <asm/simd.h>
> @@ -867,18 +868,20 @@ asmlinkage void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
>  asmlinkage void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
>  {
>  	siginfo_t info;
> -	unsigned int si_code = FPE_FIXME;
> -
> -	if (esr & FPEXC_IOF)
> -		si_code = FPE_FLTINV;
> -	else if (esr & FPEXC_DZF)
> -		si_code = FPE_FLTDIV;
> -	else if (esr & FPEXC_OFF)
> -		si_code = FPE_FLTOVF;
> -	else if (esr & FPEXC_UFF)
> -		si_code = FPE_FLTUND;
> -	else if (esr & FPEXC_IXF)
> -		si_code = FPE_FLTRES;
> +	unsigned int si_code = FPE_FLTUNK;
> +
> +	if (esr & ESR_ELx_FP_EXC_TFV) {
> +		if (esr & FPEXC_IOF)
> +			si_code = FPE_FLTINV;
> +		else if (esr & FPEXC_DZF)
> +			si_code = FPE_FLTDIV;
> +		else if (esr & FPEXC_OFF)
> +			si_code = FPE_FLTOVF;
> +		else if (esr & FPEXC_UFF)
> +			si_code = FPE_FLTUND;
> +		else if (esr & FPEXC_IXF)
> +			si_code = FPE_FLTRES;
> +	}
>  
>  	memset(&info, 0, sizeof(info));
>  	info.si_signo = SIGFPE;

[PATCH v2 3/3] arm64: signal: Ensure si_code is valid for all fault signals

[Dave Martin]

Currently, as reported by Eric, an invalid si_code value 0 is
passed in many signals delivered to userspace in response to faults
and other kernel errors.  Typically 0 is passed when the fault is
insufficiently diagnosable or when there does not appear to be any
sensible alternative value to choose.

This appears to violate POSIX, and is intuitively wrong for at
least two reasons arising from the fact that 0 == SI_USER:

 1) si_code is a union selector, and SI_USER (and si_code <= 0 in
    general) implies the existence of a different set of fields
    (siginfo._kill) from that which exists for a fault signal
    (siginfo._sigfault).  However, the code raising the signal
    typically writes only the _sigfault fields, and the _kill
    fields make no sense in this case.

    Thus when userspace sees si_code == 0 (SI_USER) it may
    legitimately inspect fields in the inactive union member _kill
    and obtain garbage as a result.

    There appears to be software in the wild relying on this,
    albeit generally only for printing diagnostic messages.

 2) Software that wants to be robust against spurious signals may
    discard signals where si_code == SI_USER (or <= 0), or may
    filter such signals based on the si_uid and si_pid fields of
    siginfo._sigkill.  In the case of fault signals, this means
    that important (and usually fatal) error conditions may be
    silently ignored.

In practice, many of the faults for which arm64 passes si_code == 0
are undiagnosable conditions such as exceptions with syndrome
values in ESR_ELx to which the architecture does not yet assign any
meaning, or conditions indicative of a bug or error in the kernel
or system and thus that are unrecoverable and should never occur in
normal operation.

The approach taken in this patch is to translate all such
undiagnosable or "impossible" synchronous fault conditions to
SIGKILL, since these are at least probably localisable to a single
process.  Some of these conditions should really result in a kernel
panic, but due to the lack of diagnostic information it is
difficult to be certain: this patch does not add any calls to
panic(), but this could change later if justified.

Although si_code will not reach userspace in the case of SIGKILL,
it is still desirable to pass a nonzero value so that the common
siginfo handling code can detect incorrect use of si_code == 0
without false positives.  In this case the si_code dependent
siginfo fields will not be correctly initialised, but since they
are not passed to userspace I deem this not to matter.

A few faults can reasonably occur in realistic userspace scenarios,
and _should_ raise a regular, handleable (but perhaps not
ignorable/blockable) signal: for these, this patch attempts to
choose a suitable standard si_code value for the raised signal in
each case instead of 0.

arm64 was the only arch to define a BUS_FIXME code, so after this
patch nobody defines it.  This patch therefore also removes the
relevant code from siginfo_layout().

Cc: James Morse <james.morse@arm.com>
Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>

---

Changes since RFC v2:

 * Squashed in revert of the appropriate bits of Eric's BUS_/TRAP_FIXME
   stuff.

 * Propagated the fault_info[] sig and code vaules through do_sea(),
   which previously was ignoring them.
---
 arch/arm64/include/uapi/asm/siginfo.h |  14 ----
 arch/arm64/kernel/fpsimd.c            |   4 +-
 arch/arm64/mm/fault.c                 | 116 +++++++++++++++++-----------------
 kernel/signal.c                       |   4 --
 4 files changed, 60 insertions(+), 78 deletions(-)

diff --git a/arch/arm64/include/uapi/asm/siginfo.h b/arch/arm64/include/uapi/asm/siginfo.h
index 157e6a8..574d12f 100644
--- a/arch/arm64/include/uapi/asm/siginfo.h
+++ b/arch/arm64/include/uapi/asm/siginfo.h
@@ -21,18 +21,4 @@
 
 #include <asm-generic/siginfo.h>
 
-/*
- * SIGBUS si_codes
- */
-#ifdef __KERNEL__
-#define BUS_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
-/*
- * SIGTRAP si_codes
- */
-#ifdef __KERNEL__
-#define TRAP_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
 #endif
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 9040038..dc93aa4 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -286,8 +286,8 @@ static void task_fpsimd_save(void)
 				 * re-enter user with corrupt state.
 				 * There's no way to recover, so kill it:
 				 */
-				force_signal_inject(
-					SIGKILL, 0, current_pt_regs(), 0);
+				force_signal_inject(SIGKILL, SI_KERNEL,
+						    current_pt_regs(), 0);
 				return;
 			}
 
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index bff1155..c7c85c3 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -600,9 +600,9 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 			nmi_exit();
 	}
 
-	info.si_signo = SIGBUS;
+	info.si_signo = inf->sig;
 	info.si_errno = 0;
-	info.si_code  = BUS_FIXME;
+	info.si_code  = inf->code;
 	if (esr & ESR_ELx_FnV)
 		info.si_addr = NULL;
 	else
@@ -613,70 +613,70 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 }
 
 static const struct fault_info fault_info[] = {
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"ttbr address size fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"level 1 address size fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"level 2 address size fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"level 3 address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"ttbr address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"level 1 address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"level 2 address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"level 3 address size fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 0 translation fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 1 translation fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 2 translation fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 3 translation fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 8"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 8"			},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 1 access flag fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 2 access flag fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 3 access flag fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 12"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 12"			},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 1 permission fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 2 permission fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 3 permission fault"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"synchronous external abort"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 17"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 18"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 19"			},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 0 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 1 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 2 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 3 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"synchronous parity or ECC error" },	// Reserved when RAS is implemented
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 25"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 26"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 27"			},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 0 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 1 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 2 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 3 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 32"			},
+	{ do_sea,		SIGBUS,  BUS_OBJERR,	"synchronous external abort"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 17"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 18"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 19"			},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 0 (translation table walk)"	},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 1 (translation table walk)"	},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 2 (translation table walk)"	},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 3 (translation table walk)"	},
+	{ do_sea,		SIGBUS,  BUS_OBJERR,	"synchronous parity or ECC error" },	// Reserved when RAS is implemented
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 25"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 26"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 27"			},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 0 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 1 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 2 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 3 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 32"			},
 	{ do_alignment_fault,	SIGBUS,  BUS_ADRALN,	"alignment fault"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 34"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 35"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 36"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 37"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 38"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 39"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 40"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 41"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 42"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 43"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 44"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 45"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 46"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 47"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"TLB conflict abort"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"Unsupported atomic hardware update fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 50"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 51"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"implementation fault (lockdown abort)" },
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"implementation fault (unsupported exclusive)" },
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 54"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 55"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 56"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 57"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 58" 			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 59"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 60"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"section domain fault"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"page domain fault"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 63"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 34"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 35"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 36"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 37"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 38"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 39"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 40"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 41"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 42"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 43"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 44"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 45"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 46"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 47"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"TLB conflict abort"		},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"Unsupported atomic hardware update fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 50"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 51"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"implementation fault (lockdown abort)" },
+	{ do_bad,		SIGBUS,  BUS_OBJERR,	"implementation fault (unsupported exclusive)" },
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 54"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 55"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 56"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 57"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 58" 			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 59"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 60"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"section domain fault"		},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"page domain fault"		},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 63"			},
 };
 
 int handle_guest_sea(phys_addr_t addr, unsigned int esr)
@@ -774,11 +774,11 @@ static struct fault_info __refdata debug_fault_info[] = {
 	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware breakpoint"	},
 	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware single-step"	},
 	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware watchpoint"	},
-	{ do_bad,	SIGBUS,		BUS_FIXME,	"unknown 3"		},
+	{ do_bad,	SIGKILL,	SI_KERNEL,	"unknown 3"		},
 	{ do_bad,	SIGTRAP,	TRAP_BRKPT,	"aarch32 BKPT"		},
-	{ do_bad,	SIGTRAP,	TRAP_FIXME,	"aarch32 vector catch"	},
+	{ do_bad,	SIGKILL,	SI_KERNEL,	"aarch32 vector catch"	},
 	{ early_brk64,	SIGTRAP,	TRAP_BRKPT,	"aarch64 BRK"		},
-	{ do_bad,	SIGBUS,		BUS_FIXME,	"unknown 7"		},
+	{ do_bad,	SIGKILL,	SI_KERNEL,	"unknown 7"		},
 };
 
 void __init hook_debug_fault_code(int nr,
diff --git a/kernel/signal.c b/kernel/signal.c
index c6e4c83d..049a482 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2844,10 +2844,6 @@ enum siginfo_layout siginfo_layout(int sig, int si_code)
 		if ((sig == SIGFPE) && (si_code == FPE_FIXME))
 			layout = SIL_FAULT;
 #endif
-#ifdef BUS_FIXME
-		if ((sig == SIGBUS) && (si_code == BUS_FIXME))
-			layout = SIL_FAULT;
-#endif
 	}
 	return layout;
 }
-- 
2.1.4

[PATCH v2 3/3] arm64: signal: Ensure si_code is valid for all fault signals

[Dave Martin]

Currently, as reported by Eric, an invalid si_code value 0 is
passed in many signals delivered to userspace in response to faults
and other kernel errors.  Typically 0 is passed when the fault is
insufficiently diagnosable or when there does not appear to be any
sensible alternative value to choose.

This appears to violate POSIX, and is intuitively wrong for at
least two reasons arising from the fact that 0 == SI_USER:

 1) si_code is a union selector, and SI_USER (and si_code <= 0 in
    general) implies the existence of a different set of fields
    (siginfo._kill) from that which exists for a fault signal
    (siginfo._sigfault).  However, the code raising the signal
    typically writes only the _sigfault fields, and the _kill
    fields make no sense in this case.

    Thus when userspace sees si_code == 0 (SI_USER) it may
    legitimately inspect fields in the inactive union member _kill
    and obtain garbage as a result.

    There appears to be software in the wild relying on this,
    albeit generally only for printing diagnostic messages.

 2) Software that wants to be robust against spurious signals may
    discard signals where si_code == SI_USER (or <= 0), or may
    filter such signals based on the si_uid and si_pid fields of
    siginfo._sigkill.  In the case of fault signals, this means
    that important (and usually fatal) error conditions may be
    silently ignored.

In practice, many of the faults for which arm64 passes si_code == 0
are undiagnosable conditions such as exceptions with syndrome
values in ESR_ELx to which the architecture does not yet assign any
meaning, or conditions indicative of a bug or error in the kernel
or system and thus that are unrecoverable and should never occur in
normal operation.

The approach taken in this patch is to translate all such
undiagnosable or "impossible" synchronous fault conditions to
SIGKILL, since these are at least probably localisable to a single
process.  Some of these conditions should really result in a kernel
panic, but due to the lack of diagnostic information it is
difficult to be certain: this patch does not add any calls to
panic(), but this could change later if justified.

Although si_code will not reach userspace in the case of SIGKILL,
it is still desirable to pass a nonzero value so that the common
siginfo handling code can detect incorrect use of si_code == 0
without false positives.  In this case the si_code dependent
siginfo fields will not be correctly initialised, but since they
are not passed to userspace I deem this not to matter.

A few faults can reasonably occur in realistic userspace scenarios,
and _should_ raise a regular, handleable (but perhaps not
ignorable/blockable) signal: for these, this patch attempts to
choose a suitable standard si_code value for the raised signal in
each case instead of 0.

arm64 was the only arch to define a BUS_FIXME code, so after this
patch nobody defines it.  This patch therefore also removes the
relevant code from siginfo_layout().

Cc: James Morse <james.morse@arm.com>
Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>

---

Changes since RFC v2:

 * Squashed in revert of the appropriate bits of Eric's BUS_/TRAP_FIXME
   stuff.

 * Propagated the fault_info[] sig and code vaules through do_sea(),
   which previously was ignoring them.
---
 arch/arm64/include/uapi/asm/siginfo.h |  14 ----
 arch/arm64/kernel/fpsimd.c            |   4 +-
 arch/arm64/mm/fault.c                 | 116 +++++++++++++++++-----------------
 kernel/signal.c                       |   4 --
 4 files changed, 60 insertions(+), 78 deletions(-)

diff --git a/arch/arm64/include/uapi/asm/siginfo.h b/arch/arm64/include/uapi/asm/siginfo.h
index 157e6a8..574d12f 100644
--- a/arch/arm64/include/uapi/asm/siginfo.h
+++ b/arch/arm64/include/uapi/asm/siginfo.h
@@ -21,18 +21,4 @@
 
 #include <asm-generic/siginfo.h>
 
-/*
- * SIGBUS si_codes
- */
-#ifdef __KERNEL__
-#define BUS_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
-/*
- * SIGTRAP si_codes
- */
-#ifdef __KERNEL__
-#define TRAP_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
 #endif
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 9040038..dc93aa4 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -286,8 +286,8 @@ static void task_fpsimd_save(void)
 				 * re-enter user with corrupt state.
 				 * There's no way to recover, so kill it:
 				 */
-				force_signal_inject(
-					SIGKILL, 0, current_pt_regs(), 0);
+				force_signal_inject(SIGKILL, SI_KERNEL,
+						    current_pt_regs(), 0);
 				return;
 			}
 
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index bff1155..c7c85c3 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -600,9 +600,9 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 			nmi_exit();
 	}
 
-	info.si_signo = SIGBUS;
+	info.si_signo = inf->sig;
 	info.si_errno = 0;
-	info.si_code  = BUS_FIXME;
+	info.si_code  = inf->code;
 	if (esr & ESR_ELx_FnV)
 		info.si_addr = NULL;
 	else
@@ -613,70 +613,70 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 }
 
 static const struct fault_info fault_info[] = {
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"ttbr address size fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"level 1 address size fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"level 2 address size fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"level 3 address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"ttbr address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"level 1 address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"level 2 address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"level 3 address size fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 0 translation fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 1 translation fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 2 translation fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 3 translation fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 8"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 8"			},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 1 access flag fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 2 access flag fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 3 access flag fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 12"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 12"			},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 1 permission fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 2 permission fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 3 permission fault"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"synchronous external abort"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 17"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 18"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 19"			},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 0 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 1 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 2 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 3 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"synchronous parity or ECC error" },	// Reserved when RAS is implemented
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 25"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 26"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 27"			},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 0 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 1 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 2 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 3 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 32"			},
+	{ do_sea,		SIGBUS,  BUS_OBJERR,	"synchronous external abort"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 17"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 18"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 19"			},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 0 (translation table walk)"	},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 1 (translation table walk)"	},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 2 (translation table walk)"	},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 3 (translation table walk)"	},
+	{ do_sea,		SIGBUS,  BUS_OBJERR,	"synchronous parity or ECC error" },	// Reserved when RAS is implemented
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 25"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 26"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 27"			},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 0 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 1 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 2 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 3 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 32"			},
 	{ do_alignment_fault,	SIGBUS,  BUS_ADRALN,	"alignment fault"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 34"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 35"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 36"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 37"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 38"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 39"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 40"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 41"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 42"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 43"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 44"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 45"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 46"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 47"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"TLB conflict abort"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"Unsupported atomic hardware update fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 50"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 51"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"implementation fault (lockdown abort)" },
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"implementation fault (unsupported exclusive)" },
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 54"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 55"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 56"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 57"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 58" 			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 59"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 60"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"section domain fault"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"page domain fault"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 63"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 34"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 35"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 36"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 37"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 38"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 39"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 40"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 41"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 42"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 43"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 44"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 45"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 46"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 47"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"TLB conflict abort"		},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"Unsupported atomic hardware update fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 50"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 51"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"implementation fault (lockdown abort)" },
+	{ do_bad,		SIGBUS,  BUS_OBJERR,	"implementation fault (unsupported exclusive)" },
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 54"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 55"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 56"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 57"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 58" 			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 59"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 60"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"section domain fault"		},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"page domain fault"		},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 63"			},
 };
 
 int handle_guest_sea(phys_addr_t addr, unsigned int esr)
@@ -774,11 +774,11 @@ static struct fault_info __refdata debug_fault_info[] = {
 	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware breakpoint"	},
 	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware single-step"	},
 	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware watchpoint"	},
-	{ do_bad,	SIGBUS,		BUS_FIXME,	"unknown 3"		},
+	{ do_bad,	SIGKILL,	SI_KERNEL,	"unknown 3"		},
 	{ do_bad,	SIGTRAP,	TRAP_BRKPT,	"aarch32 BKPT"		},
-	{ do_bad,	SIGTRAP,	TRAP_FIXME,	"aarch32 vector catch"	},
+	{ do_bad,	SIGKILL,	SI_KERNEL,	"aarch32 vector catch"	},
 	{ early_brk64,	SIGTRAP,	TRAP_BRKPT,	"aarch64 BRK"		},
-	{ do_bad,	SIGBUS,		BUS_FIXME,	"unknown 7"		},
+	{ do_bad,	SIGKILL,	SI_KERNEL,	"unknown 7"		},
 };
 
 void __init hook_debug_fault_code(int nr,
diff --git a/kernel/signal.c b/kernel/signal.c
index c6e4c83d..049a482 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2844,10 +2844,6 @@ enum siginfo_layout siginfo_layout(int sig, int si_code)
 		if ((sig == SIGFPE) && (si_code == FPE_FIXME))
 			layout = SIL_FAULT;
 #endif
-#ifdef BUS_FIXME
-		if ((sig == SIGBUS) && (si_code == BUS_FIXME))
-			layout = SIL_FAULT;
-#endif
 	}
 	return layout;
 }
-- 
2.1.4

[PATCH v2 3/3] arm64: signal: Ensure si_code is valid for all fault signals

[Dave Martin]

Currently, as reported by Eric, an invalid si_code value 0 is
passed in many signals delivered to userspace in response to faults
and other kernel errors.  Typically 0 is passed when the fault is
insufficiently diagnosable or when there does not appear to be any
sensible alternative value to choose.

This appears to violate POSIX, and is intuitively wrong for at
least two reasons arising from the fact that 0 == SI_USER:

 1) si_code is a union selector, and SI_USER (and si_code <= 0 in
    general) implies the existence of a different set of fields
    (siginfo._kill) from that which exists for a fault signal
    (siginfo._sigfault).  However, the code raising the signal
    typically writes only the _sigfault fields, and the _kill
    fields make no sense in this case.

    Thus when userspace sees si_code == 0 (SI_USER) it may
    legitimately inspect fields in the inactive union member _kill
    and obtain garbage as a result.

    There appears to be software in the wild relying on this,
    albeit generally only for printing diagnostic messages.

 2) Software that wants to be robust against spurious signals may
    discard signals where si_code == SI_USER (or <= 0), or may
    filter such signals based on the si_uid and si_pid fields of
    siginfo._sigkill.  In the case of fault signals, this means
    that important (and usually fatal) error conditions may be
    silently ignored.

In practice, many of the faults for which arm64 passes si_code == 0
are undiagnosable conditions such as exceptions with syndrome
values in ESR_ELx to which the architecture does not yet assign any
meaning, or conditions indicative of a bug or error in the kernel
or system and thus that are unrecoverable and should never occur in
normal operation.

The approach taken in this patch is to translate all such
undiagnosable or "impossible" synchronous fault conditions to
SIGKILL, since these are at least probably localisable to a single
process.  Some of these conditions should really result in a kernel
panic, but due to the lack of diagnostic information it is
difficult to be certain: this patch does not add any calls to
panic(), but this could change later if justified.

Although si_code will not reach userspace in the case of SIGKILL,
it is still desirable to pass a nonzero value so that the common
siginfo handling code can detect incorrect use of si_code == 0
without false positives.  In this case the si_code dependent
siginfo fields will not be correctly initialised, but since they
are not passed to userspace I deem this not to matter.

A few faults can reasonably occur in realistic userspace scenarios,
and _should_ raise a regular, handleable (but perhaps not
ignorable/blockable) signal: for these, this patch attempts to
choose a suitable standard si_code value for the raised signal in
each case instead of 0.

arm64 was the only arch to define a BUS_FIXME code, so after this
patch nobody defines it.  This patch therefore also removes the
relevant code from siginfo_layout().

Cc: James Morse <james.morse@arm.com>
Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>

---

Changes since RFC v2:

 * Squashed in revert of the appropriate bits of Eric's BUS_/TRAP_FIXME
   stuff.

 * Propagated the fault_info[] sig and code vaules through do_sea(),
   which previously was ignoring them.
---
 arch/arm64/include/uapi/asm/siginfo.h |  14 ----
 arch/arm64/kernel/fpsimd.c            |   4 +-
 arch/arm64/mm/fault.c                 | 116 +++++++++++++++++-----------------
 kernel/signal.c                       |   4 --
 4 files changed, 60 insertions(+), 78 deletions(-)

diff --git a/arch/arm64/include/uapi/asm/siginfo.h b/arch/arm64/include/uapi/asm/siginfo.h
index 157e6a8..574d12f 100644
--- a/arch/arm64/include/uapi/asm/siginfo.h
+++ b/arch/arm64/include/uapi/asm/siginfo.h
@@ -21,18 +21,4 @@
 
 #include <asm-generic/siginfo.h>
 
-/*
- * SIGBUS si_codes
- */
-#ifdef __KERNEL__
-#define BUS_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
-/*
- * SIGTRAP si_codes
- */
-#ifdef __KERNEL__
-#define TRAP_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
 #endif
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 9040038..dc93aa4 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -286,8 +286,8 @@ static void task_fpsimd_save(void)
 				 * re-enter user with corrupt state.
 				 * There's no way to recover, so kill it:
 				 */
-				force_signal_inject(
-					SIGKILL, 0, current_pt_regs(), 0);
+				force_signal_inject(SIGKILL, SI_KERNEL,
+						    current_pt_regs(), 0);
 				return;
 			}
 
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index bff1155..c7c85c3 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -600,9 +600,9 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 			nmi_exit();
 	}
 
-	info.si_signo = SIGBUS;
+	info.si_signo = inf->sig;
 	info.si_errno = 0;
-	info.si_code  = BUS_FIXME;
+	info.si_code  = inf->code;
 	if (esr & ESR_ELx_FnV)
 		info.si_addr = NULL;
 	else
@@ -613,70 +613,70 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 }
 
 static const struct fault_info fault_info[] = {
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"ttbr address size fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"level 1 address size fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"level 2 address size fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"level 3 address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"ttbr address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"level 1 address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"level 2 address size fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"level 3 address size fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 0 translation fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 1 translation fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 2 translation fault"	},
 	{ do_translation_fault,	SIGSEGV, SEGV_MAPERR,	"level 3 translation fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 8"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 8"			},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 1 access flag fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 2 access flag fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 3 access flag fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 12"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 12"			},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 1 permission fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 2 permission fault"	},
 	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 3 permission fault"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"synchronous external abort"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 17"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 18"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 19"			},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 0 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 1 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 2 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 3 (translation table walk)"	},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"synchronous parity or ECC error" },	// Reserved when RAS is implemented
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 25"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 26"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 27"			},
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 0 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 1 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 2 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_sea,		SIGBUS,  BUS_FIXME,	"level 3 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 32"			},
+	{ do_sea,		SIGBUS,  BUS_OBJERR,	"synchronous external abort"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 17"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 18"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 19"			},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 0 (translation table walk)"	},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 1 (translation table walk)"	},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 2 (translation table walk)"	},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 3 (translation table walk)"	},
+	{ do_sea,		SIGBUS,  BUS_OBJERR,	"synchronous parity or ECC error" },	// Reserved when RAS is implemented
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 25"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 26"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 27"			},
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 0 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 1 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 2 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_sea,		SIGKILL, SI_KERNEL,	"level 3 synchronous parity error (translation table walk)"	},	// Reserved when RAS is implemented
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 32"			},
 	{ do_alignment_fault,	SIGBUS,  BUS_ADRALN,	"alignment fault"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 34"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 35"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 36"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 37"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 38"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 39"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 40"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 41"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 42"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 43"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 44"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 45"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 46"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 47"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"TLB conflict abort"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"Unsupported atomic hardware update fault"	},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 50"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 51"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"implementation fault (lockdown abort)" },
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"implementation fault (unsupported exclusive)" },
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 54"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 55"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 56"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 57"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 58" 			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 59"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 60"			},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"section domain fault"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"page domain fault"		},
-	{ do_bad,		SIGBUS,  BUS_FIXME,	"unknown 63"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 34"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 35"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 36"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 37"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 38"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 39"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 40"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 41"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 42"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 43"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 44"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 45"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 46"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 47"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"TLB conflict abort"		},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"Unsupported atomic hardware update fault"	},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 50"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 51"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"implementation fault (lockdown abort)" },
+	{ do_bad,		SIGBUS,  BUS_OBJERR,	"implementation fault (unsupported exclusive)" },
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 54"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 55"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 56"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 57"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 58" 			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 59"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 60"			},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"section domain fault"		},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"page domain fault"		},
+	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 63"			},
 };
 
 int handle_guest_sea(phys_addr_t addr, unsigned int esr)
@@ -774,11 +774,11 @@ static struct fault_info __refdata debug_fault_info[] = {
 	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware breakpoint"	},
 	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware single-step"	},
 	{ do_bad,	SIGTRAP,	TRAP_HWBKPT,	"hardware watchpoint"	},
-	{ do_bad,	SIGBUS,		BUS_FIXME,	"unknown 3"		},
+	{ do_bad,	SIGKILL,	SI_KERNEL,	"unknown 3"		},
 	{ do_bad,	SIGTRAP,	TRAP_BRKPT,	"aarch32 BKPT"		},
-	{ do_bad,	SIGTRAP,	TRAP_FIXME,	"aarch32 vector catch"	},
+	{ do_bad,	SIGKILL,	SI_KERNEL,	"aarch32 vector catch"	},
 	{ early_brk64,	SIGTRAP,	TRAP_BRKPT,	"aarch64 BRK"		},
-	{ do_bad,	SIGBUS,		BUS_FIXME,	"unknown 7"		},
+	{ do_bad,	SIGKILL,	SI_KERNEL,	"unknown 7"		},
 };
 
 void __init hook_debug_fault_code(int nr,
diff --git a/kernel/signal.c b/kernel/signal.c
index c6e4c83d..049a482 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2844,10 +2844,6 @@ enum siginfo_layout siginfo_layout(int sig, int si_code)
 		if ((sig == SIGFPE) && (si_code == FPE_FIXME))
 			layout = SIL_FAULT;
 #endif
-#ifdef BUS_FIXME
-		if ((sig == SIGBUS) && (si_code == BUS_FIXME))
-			layout = SIL_FAULT;
-#endif
 	}
 	return layout;
 }
-- 
2.1.4

Re: [PATCH v2 3/3] arm64: signal: Ensure si_code is valid for all fault signals

[Will Deacon]

Hi Dave,

On Thu, Mar 01, 2018 at 05:44:08PM +0000, Dave Martin wrote:
> Currently, as reported by Eric, an invalid si_code value 0 is
> passed in many signals delivered to userspace in response to faults
> and other kernel errors.  Typically 0 is passed when the fault is
> insufficiently diagnosable or when there does not appear to be any
> sensible alternative value to choose.

This looks good to me. Please could you rebase it on top of for-next/core,
so that I can apply it for 4.17? The other two patches in the series need
an Ack for the core changes, so it would be worth dealing with those
separately imo.

Cheers,

Will

[PATCH v2 3/3] arm64: signal: Ensure si_code is valid for all fault signals

[Will Deacon]

Hi Dave,

On Thu, Mar 01, 2018 at 05:44:08PM +0000, Dave Martin wrote:
> Currently, as reported by Eric, an invalid si_code value 0 is
> passed in many signals delivered to userspace in response to faults
> and other kernel errors.  Typically 0 is passed when the fault is
> insufficiently diagnosable or when there does not appear to be any
> sensible alternative value to choose.

This looks good to me. Please could you rebase it on top of for-next/core,
so that I can apply it for 4.17? The other two patches in the series need
an Ack for the core changes, so it would be worth dealing with those
separately imo.

Cheers,

Will

Re: [PATCH v2 3/3] arm64: signal: Ensure si_code is valid for all fault signals

[Will Deacon]

Hi Dave,

On Thu, Mar 01, 2018 at 05:44:08PM +0000, Dave Martin wrote:
> Currently, as reported by Eric, an invalid si_code value 0 is
> passed in many signals delivered to userspace in response to faults
> and other kernel errors.  Typically 0 is passed when the fault is
> insufficiently diagnosable or when there does not appear to be any
> sensible alternative value to choose.

This looks good to me. Please could you rebase it on top of for-next/core,
so that I can apply it for 4.17? The other two patches in the series need
an Ack for the core changes, so it would be worth dealing with those
separately imo.

Cheers,

Will