[PATCH 0/4] MIPS: Syscall tracing fixes

[PATCH 0/4] MIPS: Syscall tracing fixes

[James Hogan]

These patches fix several issues in the MIPS syscall tracing support.
They are based on mips-for-linux-next (152e63e374cd).

Patch 1 drops a harmless redundant select in Kconfig.

Patch 2 ensures erroring syscalls have negated return value in the
sys_exit trace event, so errors can be distinguished from success
(tagged for stable).

Patch 3 corrects a probably harmless inconsistency between normal
syscall error return ($a3=1) and modified error return via
syscall_set_return_value() ($a3=-1), e.g. due to seccomp
SECCOMP_RET_ERRNO.

Patch 4 fixes the probably harmless broken error return from negative
syscall numbers when syscall tracing is enabled.

Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org

James Hogan (4):
  MIPS: Drop duplicate HAVE_SYSCALL_TRACEPOINTS select
  MIPS: Negate error syscall return in trace
  MIPS: Correct forced syscall errors
  MIPS: Traced negative syscalls should return -ENOSYS

 arch/mips/Kconfig               |  1 -
 arch/mips/include/asm/syscall.h |  2 +-
 arch/mips/kernel/ptrace.c       |  9 ++++++++-
 3 files changed, 9 insertions(+), 3 deletions(-)

-- 
git-series 0.8.10

[PATCH 0/4] MIPS: Syscall tracing fixes

[James Hogan]

These patches fix several issues in the MIPS syscall tracing support.
They are based on mips-for-linux-next (152e63e374cd).

Patch 1 drops a harmless redundant select in Kconfig.

Patch 2 ensures erroring syscalls have negated return value in the
sys_exit trace event, so errors can be distinguished from success
(tagged for stable).

Patch 3 corrects a probably harmless inconsistency between normal
syscall error return ($a3=1) and modified error return via
syscall_set_return_value() ($a3=-1), e.g. due to seccomp
SECCOMP_RET_ERRNO.

Patch 4 fixes the probably harmless broken error return from negative
syscall numbers when syscall tracing is enabled.

Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org

James Hogan (4):
  MIPS: Drop duplicate HAVE_SYSCALL_TRACEPOINTS select
  MIPS: Negate error syscall return in trace
  MIPS: Correct forced syscall errors
  MIPS: Traced negative syscalls should return -ENOSYS

 arch/mips/Kconfig               |  1 -
 arch/mips/include/asm/syscall.h |  2 +-
 arch/mips/kernel/ptrace.c       |  9 ++++++++-
 3 files changed, 9 insertions(+), 3 deletions(-)

-- 
git-series 0.8.10

[PATCH 1/4] MIPS: Drop duplicate HAVE_SYSCALL_TRACEPOINTS select

[James Hogan]

MIPS selects HAVE_SYSCALL_TRACEPOINTS twice. The first was added back in
v3.13 by commit 2d7bf993e073 ("MIPS: ftrace: Add support for syscall
tracepoints."), but then a second redundant one was added in v4.2 by
commit fb59e394c30c ("MIPS: ftrace: Enable support for syscall
tracepoints.").

Drop the duplicate select.

Fixes: fb59e394c30c ("MIPS: ftrace: Enable support for syscall tracepoints.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---
 arch/mips/Kconfig | 1 -
 1 file changed, 0 insertions(+), 1 deletion(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 609986e8b21e..55e48a3e7f05 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -64,7 +64,6 @@ config MIPS
 	select HAVE_PERF_EVENTS
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_SYSCALL_TRACEPOINTS
-	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select IRQ_FORCED_THREADING
 	select MODULES_USE_ELF_RELA if MODULES && 64BIT
-- 
git-series 0.8.10

[PATCH 1/4] MIPS: Drop duplicate HAVE_SYSCALL_TRACEPOINTS select

[James Hogan]

MIPS selects HAVE_SYSCALL_TRACEPOINTS twice. The first was added back in
v3.13 by commit 2d7bf993e073 ("MIPS: ftrace: Add support for syscall
tracepoints."), but then a second redundant one was added in v4.2 by
commit fb59e394c30c ("MIPS: ftrace: Enable support for syscall
tracepoints.").

Drop the duplicate select.

Fixes: fb59e394c30c ("MIPS: ftrace: Enable support for syscall tracepoints.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---
 arch/mips/Kconfig | 1 -
 1 file changed, 0 insertions(+), 1 deletion(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 609986e8b21e..55e48a3e7f05 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -64,7 +64,6 @@ config MIPS
 	select HAVE_PERF_EVENTS
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_SYSCALL_TRACEPOINTS
-	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_VIRT_CPU_ACCOUNTING_GEN
 	select IRQ_FORCED_THREADING
 	select MODULES_USE_ELF_RELA if MODULES && 64BIT
-- 
git-series 0.8.10

[PATCH 2/4] MIPS: Negate error syscall return in trace

[James Hogan]

The sys_exit trace event takes a single return value for the system
call, which MIPS passes the value of the $v0 (result) register, however
MIPS returns positive error codes in $v0 with $a3 specifying that $v0
contains an error code. As a result erroring system calls are traced
returning positive error numbers that can't always be distinguished from
success.

Use regs_return_value() to negate the error code if $a3 is set.

Fixes: 1d7bf993e073 ("MIPS: ftrace: Add support for syscall tracepoints.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-mips@linux-mips.org
Cc: <stable@vger.kernel.org> # 3.13+
---
 arch/mips/kernel/ptrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index ba3b1f771256..8e2ea86dc23e 100644
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -913,7 +913,7 @@ asmlinkage void syscall_trace_leave(struct pt_regs *regs)
 	audit_syscall_exit(regs);
 
 	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
-		trace_sys_exit(regs, regs->regs[2]);
+		trace_sys_exit(regs, regs_return_value(regs));
 
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
 		tracehook_report_syscall_exit(regs, 0);
-- 
git-series 0.8.10

[PATCH 2/4] MIPS: Negate error syscall return in trace

[James Hogan]

The sys_exit trace event takes a single return value for the system
call, which MIPS passes the value of the $v0 (result) register, however
MIPS returns positive error codes in $v0 with $a3 specifying that $v0
contains an error code. As a result erroring system calls are traced
returning positive error numbers that can't always be distinguished from
success.

Use regs_return_value() to negate the error code if $a3 is set.

Fixes: 1d7bf993e073 ("MIPS: ftrace: Add support for syscall tracepoints.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-mips@linux-mips.org
Cc: <stable@vger.kernel.org> # 3.13+
---
 arch/mips/kernel/ptrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index ba3b1f771256..8e2ea86dc23e 100644
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -913,7 +913,7 @@ asmlinkage void syscall_trace_leave(struct pt_regs *regs)
 	audit_syscall_exit(regs);
 
 	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
-		trace_sys_exit(regs, regs->regs[2]);
+		trace_sys_exit(regs, regs_return_value(regs));
 
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
 		tracehook_report_syscall_exit(regs, 0);
-- 
git-series 0.8.10

[PATCH 3/4] MIPS: Correct forced syscall errors

[James Hogan]

When the system call return value is forced to be an error (for example
due to SECCOMP_RET_ERRNO), syscall_set_return_value() puts the error
code in the return register $v0 and -1 in the error register $a3.

However normally executed system calls put 1 in the error register
rather than -1, so fix syscall_set_return_value() to be consistent with
that.

I don't anticipate that anything would have been broken by this, since
the most natural way to check the error register on MIPS would be a
conditional branch if error register is [not] equal to zero (bnez or
beqz).

Fixes: 1d7bf993e073 ("MIPS: ftrace: Add support for syscall tracepoints.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---
 arch/mips/include/asm/syscall.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/syscall.h b/arch/mips/include/asm/syscall.h
index d87882513ee3..7c713025b23f 100644
--- a/arch/mips/include/asm/syscall.h
+++ b/arch/mips/include/asm/syscall.h
@@ -85,7 +85,7 @@ static inline void syscall_set_return_value(struct task_struct *task,
 {
 	if (error) {
 		regs->regs[2] = -error;
-		regs->regs[7] = -1;
+		regs->regs[7] = 1;
 	} else {
 		regs->regs[2] = val;
 		regs->regs[7] = 0;
-- 
git-series 0.8.10

[PATCH 3/4] MIPS: Correct forced syscall errors

[James Hogan]

When the system call return value is forced to be an error (for example
due to SECCOMP_RET_ERRNO), syscall_set_return_value() puts the error
code in the return register $v0 and -1 in the error register $a3.

However normally executed system calls put 1 in the error register
rather than -1, so fix syscall_set_return_value() to be consistent with
that.

I don't anticipate that anything would have been broken by this, since
the most natural way to check the error register on MIPS would be a
conditional branch if error register is [not] equal to zero (bnez or
beqz).

Fixes: 1d7bf993e073 ("MIPS: ftrace: Add support for syscall tracepoints.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---
 arch/mips/include/asm/syscall.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/syscall.h b/arch/mips/include/asm/syscall.h
index d87882513ee3..7c713025b23f 100644
--- a/arch/mips/include/asm/syscall.h
+++ b/arch/mips/include/asm/syscall.h
@@ -85,7 +85,7 @@ static inline void syscall_set_return_value(struct task_struct *task,
 {
 	if (error) {
 		regs->regs[2] = -error;
-		regs->regs[7] = -1;
+		regs->regs[7] = 1;
 	} else {
 		regs->regs[2] = val;
 		regs->regs[7] = 0;
-- 
git-series 0.8.10

[PATCH 4/4] MIPS: Traced negative syscalls should return -ENOSYS

[James Hogan]

If a negative system call number is used when system call tracing is
enabled, syscall_trace_enter() will return that negative system call
number without having written the return value and error flag into the
pt_regs.

The caller then treats it as a cancelled system call and assumes that
the return value and error flag are already written, leaving the
negative system call number in the return register ($v0), and the 4th
system call argument in the error register ($a3).

Add a special case to detect this at the end of syscall_trace_enter(),
to set the return value to error -ENOSYS when this happens.

Fixes: d218af78492a ("MIPS: scall: Always run the seccomp syscall filters")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---
 arch/mips/kernel/ptrace.c | 7 +++++++
 1 file changed, 7 insertions(+), 0 deletions(-)

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index 8e2ea86dc23e..6dd13641a418 100644
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -894,6 +894,13 @@ asmlinkage long syscall_trace_enter(struct pt_regs *regs, long syscall)
 
 	audit_syscall_entry(syscall, regs->regs[4], regs->regs[5],
 			    regs->regs[6], regs->regs[7]);
+
+	/*
+	 * Negative syscall numbers are mistaken for rejected syscalls, but
+	 * won't have had the return value set appropriately, so we do so now.
+	 */
+	if (syscall < 0)
+		syscall_set_return_value(current, regs, -ENOSYS, 0);
 	return syscall;
 }
 
-- 
git-series 0.8.10

[PATCH 4/4] MIPS: Traced negative syscalls should return -ENOSYS

[James Hogan]

If a negative system call number is used when system call tracing is
enabled, syscall_trace_enter() will return that negative system call
number without having written the return value and error flag into the
pt_regs.

The caller then treats it as a cancelled system call and assumes that
the return value and error flag are already written, leaving the
negative system call number in the return register ($v0), and the 4th
system call argument in the error register ($a3).

Add a special case to detect this at the end of syscall_trace_enter(),
to set the return value to error -ENOSYS when this happens.

Fixes: d218af78492a ("MIPS: scall: Always run the seccomp syscall filters")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
---
 arch/mips/kernel/ptrace.c | 7 +++++++
 1 file changed, 7 insertions(+), 0 deletions(-)

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index 8e2ea86dc23e..6dd13641a418 100644
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -894,6 +894,13 @@ asmlinkage long syscall_trace_enter(struct pt_regs *regs, long syscall)
 
 	audit_syscall_entry(syscall, regs->regs[4], regs->regs[5],
 			    regs->regs[6], regs->regs[7]);
+
+	/*
+	 * Negative syscall numbers are mistaken for rejected syscalls, but
+	 * won't have had the return value set appropriately, so we do so now.
+	 */
+	if (syscall < 0)
+		syscall_set_return_value(current, regs, -ENOSYS, 0);
 	return syscall;
 }
 
-- 
git-series 0.8.10

Re: [PATCH 2/4] MIPS: Negate error syscall return in trace

[Steven Rostedt]

On Thu, 29 Jun 2017 10:12:34 +0100
James Hogan <james.hogan@imgtec.com> wrote:

> The sys_exit trace event takes a single return value for the system
> call, which MIPS passes the value of the $v0 (result) register, however
> MIPS returns positive error codes in $v0 with $a3 specifying that $v0
> contains an error code. As a result erroring system calls are traced
> returning positive error numbers that can't always be distinguished from
> success.
> 
> Use regs_return_value() to negate the error code if $a3 is set.
> 
> Fixes: 1d7bf993e073 ("MIPS: ftrace: Add support for syscall tracepoints.")
> Signed-off-by: James Hogan <james.hogan@imgtec.com>
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: linux-mips@linux-mips.org
> Cc: <stable@vger.kernel.org> # 3.13+
> ---
>  arch/mips/kernel/ptrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
> index ba3b1f771256..8e2ea86dc23e 100644
> --- a/arch/mips/kernel/ptrace.c
> +++ b/arch/mips/kernel/ptrace.c
> @@ -913,7 +913,7 @@ asmlinkage void syscall_trace_leave(struct pt_regs *regs)
>  	audit_syscall_exit(regs);
>  
>  	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
> -		trace_sys_exit(regs, regs->regs[2]);
> +		trace_sys_exit(regs, regs_return_value(regs));

Looks reasonable to me.

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

>  
>  	if (test_thread_flag(TIF_SYSCALL_TRACE))
>  		tracehook_report_syscall_exit(regs, 0);

Re: [PATCH 2/4] MIPS: Negate error syscall return in trace

[Steven Rostedt]

On Thu, 29 Jun 2017 10:12:34 +0100
James Hogan <james.hogan@imgtec.com> wrote:

> The sys_exit trace event takes a single return value for the system
> call, which MIPS passes the value of the $v0 (result) register, however
> MIPS returns positive error codes in $v0 with $a3 specifying that $v0
> contains an error code. As a result erroring system calls are traced
> returning positive error numbers that can't always be distinguished from
> success.
> 
> Use regs_return_value() to negate the error code if $a3 is set.
> 
> Fixes: 1d7bf993e073 ("MIPS: ftrace: Add support for syscall tracepoints.")
> Signed-off-by: James Hogan <james.hogan@imgtec.com>
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: linux-mips@linux-mips.org
> Cc: <stable@vger.kernel.org> # 3.13+
> ---
>  arch/mips/kernel/ptrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
> index ba3b1f771256..8e2ea86dc23e 100644
> --- a/arch/mips/kernel/ptrace.c
> +++ b/arch/mips/kernel/ptrace.c
> @@ -913,7 +913,7 @@ asmlinkage void syscall_trace_leave(struct pt_regs *regs)
>  	audit_syscall_exit(regs);
>  
>  	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
> -		trace_sys_exit(regs, regs->regs[2]);
> +		trace_sys_exit(regs, regs_return_value(regs));

Looks reasonable to me.

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

>  
>  	if (test_thread_flag(TIF_SYSCALL_TRACE))
>  		tracehook_report_syscall_exit(regs, 0);