[PATCH v2 0/8] vsyscall xonly mode

[PATCH v2 0/8] vsyscall xonly mode

[Andy Lutomirski]

Hi all-

This adds a new "xonly" mode for vsyscalls and makes it the default.
xonly is a bit more secure -- Kees knows about an exploit that relied on
read access to the vsyscall page.  It's also nicer from a paging
perspective, as it doesn't require user access to any of the kernel
address space as far as the CPU is concerned.  This would, for example,
allow a much simpler implementation of per-process vsyscall disabling.

I will follow up with two non-x86 changes that are related but have
no dependencies.

Changes from v1:
 - Minor cleanups (Kees)
 - Add a searchable message when a vsyscall read is denied (Kees)
 - The test case is vastly improved
 - Get rid of the extra gate vma object
 - Add the __ro_after_init patch

Andy Lutomirski (8):
  x86/vsyscall: Remove the vsyscall=native documentation
  x86/vsyscall: Add a new vsyscall=xonly mode
  x86/vsyscall: Show something useful on a read fault
  x86/vsyscall: Document odd SIGSEGV error code for vsyscalls
  selftests/x86/vsyscall: Verify that vsyscall=none blocks execution
  x86/vsyscall: Change the default vsyscall mode to xonly
  x86/vsyscall: Add __ro_after_init to global variables
  selftests/x86: Add a test for process_vm_readv() on the vsyscall page

 .../admin-guide/kernel-parameters.txt         |  11 +-
 arch/x86/Kconfig                              |  35 +++--
 arch/x86/entry/vsyscall/vsyscall_64.c         |  37 +++++-
 arch/x86/include/asm/vsyscall.h               |   6 +-
 arch/x86/mm/fault.c                           |  18 ++-
 tools/testing/selftests/x86/test_vsyscall.c   | 120 ++++++++++++++----
 6 files changed, 174 insertions(+), 53 deletions(-)

-- 
2.21.0

[PATCH v2 1/8] x86/vsyscall: Remove the vsyscall=native documentation

[Andy Lutomirski]

The vsyscall=native feature is gone -- remove the docs.

Fixes: 076ca272a14c ("x86/vsyscall/64: Drop "native" vsyscalls")
Cc: stable@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 138f6664b2e2..0082d1e56999 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5102,12 +5102,6 @@
 			emulate     [default] Vsyscalls turn into traps and are
 			            emulated reasonably safely.
 
-			native      Vsyscalls are native syscall instructions.
-			            This is a little bit faster than trapping
-			            and makes a few dynamic recompilers work
-			            better than they would in emulation mode.
-			            It also makes exploits much easier to write.
-
 			none        Vsyscalls don't work at all.  This makes
 			            them quite hard to use for exploits but
 			            might break your system.
-- 
2.21.0

Re: [PATCH v2 1/8] x86/vsyscall: Remove the vsyscall=native documentation

[Kees Cook]

On Wed, Jun 26, 2019 at 09:45:02PM -0700, Andy Lutomirski wrote:
> The vsyscall=native feature is gone -- remove the docs.
> 
> Fixes: 076ca272a14c ("x86/vsyscall/64: Drop "native" vsyscalls")
> Cc: stable@vger.kernel.org
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

Acked-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  Documentation/admin-guide/kernel-parameters.txt | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 138f6664b2e2..0082d1e56999 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5102,12 +5102,6 @@
>  			emulate     [default] Vsyscalls turn into traps and are
>  			            emulated reasonably safely.
>  
> -			native      Vsyscalls are native syscall instructions.
> -			            This is a little bit faster than trapping
> -			            and makes a few dynamic recompilers work
> -			            better than they would in emulation mode.
> -			            It also makes exploits much easier to write.
> -
>  			none        Vsyscalls don't work at all.  This makes
>  			            them quite hard to use for exploits but
>  			            might break your system.
> -- 
> 2.21.0
> 

-- 
Kees Cook

[tip:x86/entry] Documentation/admin: Remove the vsyscall=native documentation

[tip-bot for Andy Lutomirski]

Commit-ID:  d974ffcfb7447db5f29a4b662a3eaf99a4e1109e
Gitweb:     https://git.kernel.org/tip/d974ffcfb7447db5f29a4b662a3eaf99a4e1109e
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 26 Jun 2019 21:45:02 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 28 Jun 2019 00:04:38 +0200

Documentation/admin: Remove the vsyscall=native documentation

The vsyscall=native feature is gone -- remove the docs.

Fixes: 076ca272a14c ("x86/vsyscall/64: Drop "native" vsyscalls")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: stable@vger.kernel.org
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/d77c7105eb4c57c1a95a95b6a5b8ba194a18e764.1561610354.git.luto@kernel.org

---
 Documentation/admin-guide/kernel-parameters.txt | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 138f6664b2e2..0082d1e56999 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5102,12 +5102,6 @@
 			emulate     [default] Vsyscalls turn into traps and are
 			            emulated reasonably safely.
 
-			native      Vsyscalls are native syscall instructions.
-			            This is a little bit faster than trapping
-			            and makes a few dynamic recompilers work
-			            better than they would in emulation mode.
-			            It also makes exploits much easier to write.
-
 			none        Vsyscalls don't work at all.  This makes
 			            them quite hard to use for exploits but
 			            might break your system.

[PATCH v2 2/8] x86/vsyscall: Add a new vsyscall=xonly mode

[Andy Lutomirski]

With vsyscall emulation on, we still expose a readable vsyscall page
that contains syscall instructions that validly implement the
vsyscalls.  We need this because certain dynamic binary
instrumentation tools attempt to read the call targets of call
instructions in the instrumented code.  If the instrumented code
uses vsyscalls, then the vsyscal page needs to contain readable
code.

Unfortunately, leaving readable memory at a deterministic address
can be used to help various ASLR bypasses, so we gain some hardening
value if we disallow vsyscall reads.

Given how rarely the vsyscall page needs to be readable, add a
mechanism to make the vsyscall page be execute only.

Cc: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 .../admin-guide/kernel-parameters.txt         |  7 +++-
 arch/x86/Kconfig                              | 33 ++++++++++++++-----
 arch/x86/entry/vsyscall/vsyscall_64.c         | 16 +++++++--
 3 files changed, 44 insertions(+), 12 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0082d1e56999..be8c3a680afa 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5100,7 +5100,12 @@
 			targets for exploits that can control RIP.
 
 			emulate     [default] Vsyscalls turn into traps and are
-			            emulated reasonably safely.
+			            emulated reasonably safely.  The vsyscall
+				    page is readable.
+
+			xonly       Vsyscalls turn into traps and are
+			            emulated reasonably safely.  The vsyscall
+				    page is not readable.
 
 			none        Vsyscalls don't work at all.  This makes
 			            them quite hard to use for exploits but
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2bbbd4d1ba31..0182d2c67590 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2293,23 +2293,38 @@ choice
 	  it can be used to assist security vulnerability exploitation.
 
 	  This setting can be changed at boot time via the kernel command
-	  line parameter vsyscall=[emulate|none].
+	  line parameter vsyscall=[emulate|xonly|none].
 
 	  On a system with recent enough glibc (2.14 or newer) and no
 	  static binaries, you can say None without a performance penalty
 	  to improve security.
 
-	  If unsure, select "Emulate".
+	  If unsure, select "Emulate execution only".
 
 	config LEGACY_VSYSCALL_EMULATE
-		bool "Emulate"
+		bool "Full emulation"
 		help
-		  The kernel traps and emulates calls into the fixed
-		  vsyscall address mapping. This makes the mapping
-		  non-executable, but it still contains known contents,
-		  which could be used in certain rare security vulnerability
-		  exploits. This configuration is recommended when userspace
-		  still uses the vsyscall area.
+		  The kernel traps and emulates calls into the fixed vsyscall
+		  address mapping. This makes the mapping non-executable, but
+		  it still contains readable known contents, which could be
+		  used in certain rare security vulnerability exploits. This
+		  configuration is recommended when using legacy userspace
+		  that still uses vsyscalls along with legacy binary
+		  instrumentation tools that require code to be readable.
+
+		  An example of this type of legacy userspace is running
+		  Pin on an old binary that still uses vsyscalls.
+
+	config LEGACY_VSYSCALL_XONLY
+		bool "Emulate execution only"
+		help
+		  The kernel traps and emulates calls into the fixed vsyscall
+		  address mapping and does not allow reads.  This
+		  configuration is recommended when userspace might use the
+		  legacy vsyscall area but support for legacy binary
+		  instrumentation of legacy code is not needed.  It mitigates
+		  certain uses of the vsyscall area as an ASLR-bypassing
+		  buffer.
 
 	config LEGACY_VSYSCALL_NONE
 		bool "None"
diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index d9d81ad7a400..fedd7628f3a6 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -42,9 +42,11 @@
 #define CREATE_TRACE_POINTS
 #include "vsyscall_trace.h"
 
-static enum { EMULATE, NONE } vsyscall_mode =
+static enum { EMULATE, XONLY, NONE } vsyscall_mode =
 #ifdef CONFIG_LEGACY_VSYSCALL_NONE
 	NONE;
+#elif defined(CONFIG_LEGACY_VSYSCALL_XONLY)
+	XONLY;
 #else
 	EMULATE;
 #endif
@@ -54,6 +56,8 @@ static int __init vsyscall_setup(char *str)
 	if (str) {
 		if (!strcmp("emulate", str))
 			vsyscall_mode = EMULATE;
+		else if (!strcmp("xonly", str))
+			vsyscall_mode = XONLY;
 		else if (!strcmp("none", str))
 			vsyscall_mode = NONE;
 		else
@@ -357,12 +361,20 @@ void __init map_vsyscall(void)
 	extern char __vsyscall_page;
 	unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
 
-	if (vsyscall_mode != NONE) {
+	/*
+	 * For full emulation, the page needs to exist for real.  In
+	 * execute-only mode, there is no PTE at all backing the vsyscall
+	 * page.
+	 */
+	if (vsyscall_mode == EMULATE) {
 		__set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
 			     PAGE_KERNEL_VVAR);
 		set_vsyscall_pgtable_user_bits(swapper_pg_dir);
 	}
 
+	if (vsyscall_mode == XONLY)
+		gate_vma.vm_flags = VM_EXEC;
+
 	BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
 		     (unsigned long)VSYSCALL_ADDR);
 }
-- 
2.21.0

Re: [PATCH v2 2/8] x86/vsyscall: Add a new vsyscall=xonly mode

[Kees Cook]

On Wed, Jun 26, 2019 at 09:45:03PM -0700, Andy Lutomirski wrote:
> With vsyscall emulation on, we still expose a readable vsyscall page
> that contains syscall instructions that validly implement the
> vsyscalls.  We need this because certain dynamic binary
> instrumentation tools attempt to read the call targets of call
> instructions in the instrumented code.  If the instrumented code
> uses vsyscalls, then the vsyscal page needs to contain readable
> code.
> 
> Unfortunately, leaving readable memory at a deterministic address
> can be used to help various ASLR bypasses, so we gain some hardening
> value if we disallow vsyscall reads.
> 
> Given how rarely the vsyscall page needs to be readable, add a
> mechanism to make the vsyscall page be execute only.
> 
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  .../admin-guide/kernel-parameters.txt         |  7 +++-
>  arch/x86/Kconfig                              | 33 ++++++++++++++-----
>  arch/x86/entry/vsyscall/vsyscall_64.c         | 16 +++++++--
>  3 files changed, 44 insertions(+), 12 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 0082d1e56999..be8c3a680afa 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5100,7 +5100,12 @@
>  			targets for exploits that can control RIP.
>  
>  			emulate     [default] Vsyscalls turn into traps and are
> -			            emulated reasonably safely.
> +			            emulated reasonably safely.  The vsyscall
> +				    page is readable.
> +
> +			xonly       Vsyscalls turn into traps and are
> +			            emulated reasonably safely.  The vsyscall
> +				    page is not readable.
>  
>  			none        Vsyscalls don't work at all.  This makes
>  			            them quite hard to use for exploits but
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 2bbbd4d1ba31..0182d2c67590 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2293,23 +2293,38 @@ choice
>  	  it can be used to assist security vulnerability exploitation.
>  
>  	  This setting can be changed at boot time via the kernel command
> -	  line parameter vsyscall=[emulate|none].
> +	  line parameter vsyscall=[emulate|xonly|none].
>  
>  	  On a system with recent enough glibc (2.14 or newer) and no
>  	  static binaries, you can say None without a performance penalty
>  	  to improve security.
>  
> -	  If unsure, select "Emulate".
> +	  If unsure, select "Emulate execution only".
>  
>  	config LEGACY_VSYSCALL_EMULATE
> -		bool "Emulate"
> +		bool "Full emulation"
>  		help
> -		  The kernel traps and emulates calls into the fixed
> -		  vsyscall address mapping. This makes the mapping
> -		  non-executable, but it still contains known contents,
> -		  which could be used in certain rare security vulnerability
> -		  exploits. This configuration is recommended when userspace
> -		  still uses the vsyscall area.
> +		  The kernel traps and emulates calls into the fixed vsyscall
> +		  address mapping. This makes the mapping non-executable, but
> +		  it still contains readable known contents, which could be
> +		  used in certain rare security vulnerability exploits. This
> +		  configuration is recommended when using legacy userspace
> +		  that still uses vsyscalls along with legacy binary
> +		  instrumentation tools that require code to be readable.
> +
> +		  An example of this type of legacy userspace is running
> +		  Pin on an old binary that still uses vsyscalls.
> +
> +	config LEGACY_VSYSCALL_XONLY
> +		bool "Emulate execution only"
> +		help
> +		  The kernel traps and emulates calls into the fixed vsyscall
> +		  address mapping and does not allow reads.  This
> +		  configuration is recommended when userspace might use the
> +		  legacy vsyscall area but support for legacy binary
> +		  instrumentation of legacy code is not needed.  It mitigates
> +		  certain uses of the vsyscall area as an ASLR-bypassing
> +		  buffer.
>  
>  	config LEGACY_VSYSCALL_NONE
>  		bool "None"
> diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
> index d9d81ad7a400..fedd7628f3a6 100644
> --- a/arch/x86/entry/vsyscall/vsyscall_64.c
> +++ b/arch/x86/entry/vsyscall/vsyscall_64.c
> @@ -42,9 +42,11 @@
>  #define CREATE_TRACE_POINTS
>  #include "vsyscall_trace.h"
>  
> -static enum { EMULATE, NONE } vsyscall_mode =
> +static enum { EMULATE, XONLY, NONE } vsyscall_mode =
>  #ifdef CONFIG_LEGACY_VSYSCALL_NONE
>  	NONE;
> +#elif defined(CONFIG_LEGACY_VSYSCALL_XONLY)
> +	XONLY;
>  #else
>  	EMULATE;
>  #endif
> @@ -54,6 +56,8 @@ static int __init vsyscall_setup(char *str)
>  	if (str) {
>  		if (!strcmp("emulate", str))
>  			vsyscall_mode = EMULATE;
> +		else if (!strcmp("xonly", str))
> +			vsyscall_mode = XONLY;
>  		else if (!strcmp("none", str))
>  			vsyscall_mode = NONE;
>  		else
> @@ -357,12 +361,20 @@ void __init map_vsyscall(void)
>  	extern char __vsyscall_page;
>  	unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
>  
> -	if (vsyscall_mode != NONE) {
> +	/*
> +	 * For full emulation, the page needs to exist for real.  In
> +	 * execute-only mode, there is no PTE at all backing the vsyscall
> +	 * page.
> +	 */
> +	if (vsyscall_mode == EMULATE) {
>  		__set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
>  			     PAGE_KERNEL_VVAR);
>  		set_vsyscall_pgtable_user_bits(swapper_pg_dir);
>  	}
>  
> +	if (vsyscall_mode == XONLY)
> +		gate_vma.vm_flags = VM_EXEC;
> +
>  	BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
>  		     (unsigned long)VSYSCALL_ADDR);
>  }
> -- 
> 2.21.0
> 

-- 
Kees Cook

[tip:x86/entry] x86/vsyscall: Add a new vsyscall=xonly mode

[tip-bot for Andy Lutomirski]

Commit-ID:  bd49e16e3339f052fae05fb3e955c5db0c9c6445
Gitweb:     https://git.kernel.org/tip/bd49e16e3339f052fae05fb3e955c5db0c9c6445
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 26 Jun 2019 21:45:03 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 28 Jun 2019 00:04:38 +0200

x86/vsyscall: Add a new vsyscall=xonly mode

With vsyscall emulation on, a readable vsyscall page is still exposed that
contains syscall instructions that validly implement the vsyscalls.

This is required because certain dynamic binary instrumentation tools
attempt to read the call targets of call instructions in the instrumented
code.  If the instrumented code uses vsyscalls, then the vsyscall page needs
to contain readable code.

Unfortunately, leaving readable memory at a deterministic address can be
used to help various ASLR bypasses, so some hardening value can be gained
by disallowing vsyscall reads.

Given how rarely the vsyscall page needs to be readable, add a mechanism to
make the vsyscall page be execute only.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/d17655777c21bc09a7af1bbcf74e6f2b69a51152.1561610354.git.luto@kernel.org

---
 Documentation/admin-guide/kernel-parameters.txt |  7 +++++-
 arch/x86/Kconfig                                | 33 ++++++++++++++++++-------
 arch/x86/entry/vsyscall/vsyscall_64.c           | 16 ++++++++++--
 3 files changed, 44 insertions(+), 12 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0082d1e56999..be8c3a680afa 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5100,7 +5100,12 @@
 			targets for exploits that can control RIP.
 
 			emulate     [default] Vsyscalls turn into traps and are
-			            emulated reasonably safely.
+			            emulated reasonably safely.  The vsyscall
+				    page is readable.
+
+			xonly       Vsyscalls turn into traps and are
+			            emulated reasonably safely.  The vsyscall
+				    page is not readable.
 
 			none        Vsyscalls don't work at all.  This makes
 			            them quite hard to use for exploits but
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2bbbd4d1ba31..0182d2c67590 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2293,23 +2293,38 @@ choice
 	  it can be used to assist security vulnerability exploitation.
 
 	  This setting can be changed at boot time via the kernel command
-	  line parameter vsyscall=[emulate|none].
+	  line parameter vsyscall=[emulate|xonly|none].
 
 	  On a system with recent enough glibc (2.14 or newer) and no
 	  static binaries, you can say None without a performance penalty
 	  to improve security.
 
-	  If unsure, select "Emulate".
+	  If unsure, select "Emulate execution only".
 
 	config LEGACY_VSYSCALL_EMULATE
-		bool "Emulate"
+		bool "Full emulation"
 		help
-		  The kernel traps and emulates calls into the fixed
-		  vsyscall address mapping. This makes the mapping
-		  non-executable, but it still contains known contents,
-		  which could be used in certain rare security vulnerability
-		  exploits. This configuration is recommended when userspace
-		  still uses the vsyscall area.
+		  The kernel traps and emulates calls into the fixed vsyscall
+		  address mapping. This makes the mapping non-executable, but
+		  it still contains readable known contents, which could be
+		  used in certain rare security vulnerability exploits. This
+		  configuration is recommended when using legacy userspace
+		  that still uses vsyscalls along with legacy binary
+		  instrumentation tools that require code to be readable.
+
+		  An example of this type of legacy userspace is running
+		  Pin on an old binary that still uses vsyscalls.
+
+	config LEGACY_VSYSCALL_XONLY
+		bool "Emulate execution only"
+		help
+		  The kernel traps and emulates calls into the fixed vsyscall
+		  address mapping and does not allow reads.  This
+		  configuration is recommended when userspace might use the
+		  legacy vsyscall area but support for legacy binary
+		  instrumentation of legacy code is not needed.  It mitigates
+		  certain uses of the vsyscall area as an ASLR-bypassing
+		  buffer.
 
 	config LEGACY_VSYSCALL_NONE
 		bool "None"
diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index d9d81ad7a400..fedd7628f3a6 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -42,9 +42,11 @@
 #define CREATE_TRACE_POINTS
 #include "vsyscall_trace.h"
 
-static enum { EMULATE, NONE } vsyscall_mode =
+static enum { EMULATE, XONLY, NONE } vsyscall_mode =
 #ifdef CONFIG_LEGACY_VSYSCALL_NONE
 	NONE;
+#elif defined(CONFIG_LEGACY_VSYSCALL_XONLY)
+	XONLY;
 #else
 	EMULATE;
 #endif
@@ -54,6 +56,8 @@ static int __init vsyscall_setup(char *str)
 	if (str) {
 		if (!strcmp("emulate", str))
 			vsyscall_mode = EMULATE;
+		else if (!strcmp("xonly", str))
+			vsyscall_mode = XONLY;
 		else if (!strcmp("none", str))
 			vsyscall_mode = NONE;
 		else
@@ -357,12 +361,20 @@ void __init map_vsyscall(void)
 	extern char __vsyscall_page;
 	unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
 
-	if (vsyscall_mode != NONE) {
+	/*
+	 * For full emulation, the page needs to exist for real.  In
+	 * execute-only mode, there is no PTE at all backing the vsyscall
+	 * page.
+	 */
+	if (vsyscall_mode == EMULATE) {
 		__set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
 			     PAGE_KERNEL_VVAR);
 		set_vsyscall_pgtable_user_bits(swapper_pg_dir);
 	}
 
+	if (vsyscall_mode == XONLY)
+		gate_vma.vm_flags = VM_EXEC;
+
 	BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
 		     (unsigned long)VSYSCALL_ADDR);
 }

[PATCH v2 3/8] x86/vsyscall: Show something useful on a read fault

[Andy Lutomirski]

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/entry/vsyscall/vsyscall_64.c | 19 ++++++++++++++++++-
 arch/x86/include/asm/vsyscall.h       |  6 ++++--
 arch/x86/mm/fault.c                   | 11 +++++------
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index fedd7628f3a6..9c58ab807aeb 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -117,7 +117,8 @@ static bool write_ok_or_segv(unsigned long ptr, size_t size)
 	}
 }
 
-bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
+bool emulate_vsyscall(unsigned long error_code,
+		      struct pt_regs *regs, unsigned long address)
 {
 	struct task_struct *tsk;
 	unsigned long caller;
@@ -126,6 +127,22 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
 	long ret;
 	unsigned long orig_dx;
 
+	/* Write faults or kernel-privilege faults never get fixed up. */
+	if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
+		return false;
+
+	if (!(error_code & X86_PF_INSTR)) {
+		/* Failed vsyscall read */
+		if (vsyscall_mode == EMULATE)
+			return false;
+
+		/*
+		 * User code tried and failed to read the vsyscall page.
+		 */
+		warn_bad_vsyscall(KERN_INFO, regs, "vsyscall read attempt denied -- look up the vsyscall kernel parameter if you need a workaround");
+		return false;
+	}
+
 	/*
 	 * No point in checking CS -- the only way to get here is a user mode
 	 * trap to a high address, which means that we're in 64-bit user code.
diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index b986b2ca688a..ab60a71a8dcb 100644
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -13,10 +13,12 @@ extern void set_vsyscall_pgtable_user_bits(pgd_t *root);
  * Called on instruction fetch fault in vsyscall page.
  * Returns true if handled.
  */
-extern bool emulate_vsyscall(struct pt_regs *regs, unsigned long address);
+extern bool emulate_vsyscall(unsigned long error_code,
+			     struct pt_regs *regs, unsigned long address);
 #else
 static inline void map_vsyscall(void) {}
-static inline bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
+static inline bool emulate_vsyscall(unsigned long error_code,
+				    struct pt_regs *regs, unsigned long address)
 {
 	return false;
 }
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 46df4c6aae46..288a5462076f 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1369,16 +1369,15 @@ void do_user_addr_fault(struct pt_regs *regs,
 
 #ifdef CONFIG_X86_64
 	/*
-	 * Instruction fetch faults in the vsyscall page might need
-	 * emulation.  The vsyscall page is at a high address
-	 * (>PAGE_OFFSET), but is considered to be part of the user
-	 * address space.
+	 * Faults in the vsyscall page might need emulation.  The
+	 * vsyscall page is at a high address (>PAGE_OFFSET), but is
+	 * considered to be part of the user address space.
 	 *
 	 * The vsyscall page does not have a "real" VMA, so do this
 	 * emulation before we go searching for VMAs.
 	 */
-	if ((hw_error_code & X86_PF_INSTR) && is_vsyscall_vaddr(address)) {
-		if (emulate_vsyscall(regs, address))
+	if (is_vsyscall_vaddr(address)) {
+		if (emulate_vsyscall(hw_error_code, regs, address))
 			return;
 	}
 #endif
-- 
2.21.0

Re: [PATCH v2 3/8] x86/vsyscall: Show something useful on a read fault

[Kees Cook]

On Wed, Jun 26, 2019 at 09:45:04PM -0700, Andy Lutomirski wrote:
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  arch/x86/entry/vsyscall/vsyscall_64.c | 19 ++++++++++++++++++-
>  arch/x86/include/asm/vsyscall.h       |  6 ++++--
>  arch/x86/mm/fault.c                   | 11 +++++------
>  3 files changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
> index fedd7628f3a6..9c58ab807aeb 100644
> --- a/arch/x86/entry/vsyscall/vsyscall_64.c
> +++ b/arch/x86/entry/vsyscall/vsyscall_64.c
> @@ -117,7 +117,8 @@ static bool write_ok_or_segv(unsigned long ptr, size_t size)
>  	}
>  }
>  
> -bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
> +bool emulate_vsyscall(unsigned long error_code,
> +		      struct pt_regs *regs, unsigned long address)
>  {
>  	struct task_struct *tsk;
>  	unsigned long caller;
> @@ -126,6 +127,22 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
>  	long ret;
>  	unsigned long orig_dx;
>  
> +	/* Write faults or kernel-privilege faults never get fixed up. */
> +	if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
> +		return false;
> +
> +	if (!(error_code & X86_PF_INSTR)) {
> +		/* Failed vsyscall read */
> +		if (vsyscall_mode == EMULATE)
> +			return false;
> +
> +		/*
> +		 * User code tried and failed to read the vsyscall page.
> +		 */
> +		warn_bad_vsyscall(KERN_INFO, regs, "vsyscall read attempt denied -- look up the vsyscall kernel parameter if you need a workaround");
> +		return false;
> +	}
> +
>  	/*
>  	 * No point in checking CS -- the only way to get here is a user mode
>  	 * trap to a high address, which means that we're in 64-bit user code.
> diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
> index b986b2ca688a..ab60a71a8dcb 100644
> --- a/arch/x86/include/asm/vsyscall.h
> +++ b/arch/x86/include/asm/vsyscall.h
> @@ -13,10 +13,12 @@ extern void set_vsyscall_pgtable_user_bits(pgd_t *root);
>   * Called on instruction fetch fault in vsyscall page.
>   * Returns true if handled.
>   */
> -extern bool emulate_vsyscall(struct pt_regs *regs, unsigned long address);
> +extern bool emulate_vsyscall(unsigned long error_code,
> +			     struct pt_regs *regs, unsigned long address);
>  #else
>  static inline void map_vsyscall(void) {}
> -static inline bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
> +static inline bool emulate_vsyscall(unsigned long error_code,
> +				    struct pt_regs *regs, unsigned long address)
>  {
>  	return false;
>  }
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 46df4c6aae46..288a5462076f 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1369,16 +1369,15 @@ void do_user_addr_fault(struct pt_regs *regs,
>  
>  #ifdef CONFIG_X86_64
>  	/*
> -	 * Instruction fetch faults in the vsyscall page might need
> -	 * emulation.  The vsyscall page is at a high address
> -	 * (>PAGE_OFFSET), but is considered to be part of the user
> -	 * address space.
> +	 * Faults in the vsyscall page might need emulation.  The
> +	 * vsyscall page is at a high address (>PAGE_OFFSET), but is
> +	 * considered to be part of the user address space.
>  	 *
>  	 * The vsyscall page does not have a "real" VMA, so do this
>  	 * emulation before we go searching for VMAs.
>  	 */
> -	if ((hw_error_code & X86_PF_INSTR) && is_vsyscall_vaddr(address)) {
> -		if (emulate_vsyscall(regs, address))
> +	if (is_vsyscall_vaddr(address)) {
> +		if (emulate_vsyscall(hw_error_code, regs, address))
>  			return;
>  	}
>  #endif
> -- 
> 2.21.0
> 

-- 
Kees Cook

[tip:x86/entry] x86/vsyscall: Show something useful on a read fault

[tip-bot for Andy Lutomirski]

Commit-ID:  918ce325098a4eef99daad7b6796da33cebaf03a
Gitweb:     https://git.kernel.org/tip/918ce325098a4eef99daad7b6796da33cebaf03a
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 26 Jun 2019 21:45:04 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 28 Jun 2019 00:04:39 +0200

x86/vsyscall: Show something useful on a read fault

Just segfaulting the application when it tries to read the vsyscall page in
xonly mode is not helpful for those who need to debug it.

Emit a hint.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Link: https://lkml.kernel.org/r/8016afffe0eab497be32017ad7f6f7030dc3ba66.1561610354.git.luto@kernel.org

---
 arch/x86/entry/vsyscall/vsyscall_64.c | 19 ++++++++++++++++++-
 arch/x86/include/asm/vsyscall.h       |  6 ++++--
 arch/x86/mm/fault.c                   | 11 +++++------
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index fedd7628f3a6..9c58ab807aeb 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -117,7 +117,8 @@ static bool write_ok_or_segv(unsigned long ptr, size_t size)
 	}
 }
 
-bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
+bool emulate_vsyscall(unsigned long error_code,
+		      struct pt_regs *regs, unsigned long address)
 {
 	struct task_struct *tsk;
 	unsigned long caller;
@@ -126,6 +127,22 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
 	long ret;
 	unsigned long orig_dx;
 
+	/* Write faults or kernel-privilege faults never get fixed up. */
+	if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
+		return false;
+
+	if (!(error_code & X86_PF_INSTR)) {
+		/* Failed vsyscall read */
+		if (vsyscall_mode == EMULATE)
+			return false;
+
+		/*
+		 * User code tried and failed to read the vsyscall page.
+		 */
+		warn_bad_vsyscall(KERN_INFO, regs, "vsyscall read attempt denied -- look up the vsyscall kernel parameter if you need a workaround");
+		return false;
+	}
+
 	/*
 	 * No point in checking CS -- the only way to get here is a user mode
 	 * trap to a high address, which means that we're in 64-bit user code.
diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index b986b2ca688a..ab60a71a8dcb 100644
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -13,10 +13,12 @@ extern void set_vsyscall_pgtable_user_bits(pgd_t *root);
  * Called on instruction fetch fault in vsyscall page.
  * Returns true if handled.
  */
-extern bool emulate_vsyscall(struct pt_regs *regs, unsigned long address);
+extern bool emulate_vsyscall(unsigned long error_code,
+			     struct pt_regs *regs, unsigned long address);
 #else
 static inline void map_vsyscall(void) {}
-static inline bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
+static inline bool emulate_vsyscall(unsigned long error_code,
+				    struct pt_regs *regs, unsigned long address)
 {
 	return false;
 }
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 46df4c6aae46..288a5462076f 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1369,16 +1369,15 @@ void do_user_addr_fault(struct pt_regs *regs,
 
 #ifdef CONFIG_X86_64
 	/*
-	 * Instruction fetch faults in the vsyscall page might need
-	 * emulation.  The vsyscall page is at a high address
-	 * (>PAGE_OFFSET), but is considered to be part of the user
-	 * address space.
+	 * Faults in the vsyscall page might need emulation.  The
+	 * vsyscall page is at a high address (>PAGE_OFFSET), but is
+	 * considered to be part of the user address space.
 	 *
 	 * The vsyscall page does not have a "real" VMA, so do this
 	 * emulation before we go searching for VMAs.
 	 */
-	if ((hw_error_code & X86_PF_INSTR) && is_vsyscall_vaddr(address)) {
-		if (emulate_vsyscall(regs, address))
+	if (is_vsyscall_vaddr(address)) {
+		if (emulate_vsyscall(hw_error_code, regs, address))
 			return;
 	}
 #endif

[PATCH v2 4/8] x86/vsyscall: Document odd SIGSEGV error code for vsyscalls

[Andy Lutomirski]

Even if vsyscall=none, we report uer page faults on the vsyscall
page as though the PROT bit in the error code was set.  Add a
comment explaining why this is probably okay and display the value
in the test case.

While we're at it, explain why our behavior is correct with respect
to PKRU.

This also modifies the selftest to print the odd error code so that
you can run the selftest and see that the behavior is odd.

If anyone really cares about more accurate emulation, we could
change the behavior.

Cc: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/mm/fault.c                         | 7 +++++++
 tools/testing/selftests/x86/test_vsyscall.c | 9 ++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 288a5462076f..58e4f1f00bbc 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -710,6 +710,10 @@ static void set_signal_archinfo(unsigned long address,
 	 * To avoid leaking information about the kernel page
 	 * table layout, pretend that user-mode accesses to
 	 * kernel addresses are always protection faults.
+	 *
+	 * NB: This means that failed vsyscalls with vsyscall=none
+	 * will have the PROT bit.  This doesn't leak any
+	 * information and does not appear to cause any problems.
 	 */
 	if (address >= TASK_SIZE_MAX)
 		error_code |= X86_PF_PROT;
@@ -1375,6 +1379,9 @@ void do_user_addr_fault(struct pt_regs *regs,
 	 *
 	 * The vsyscall page does not have a "real" VMA, so do this
 	 * emulation before we go searching for VMAs.
+	 *
+	 * PKRU never rejects instruction fetches, so we don't need
+	 * to consider the PF_PK bit.
 	 */
 	if (is_vsyscall_vaddr(address)) {
 		if (emulate_vsyscall(hw_error_code, regs, address))
diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
index 0b4f1cc2291c..4c9a8d76dba0 100644
--- a/tools/testing/selftests/x86/test_vsyscall.c
+++ b/tools/testing/selftests/x86/test_vsyscall.c
@@ -183,9 +183,13 @@ static inline long sys_getcpu(unsigned * cpu, unsigned * node,
 }
 
 static jmp_buf jmpbuf;
+static volatile unsigned long segv_err;
 
 static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
 {
+	ucontext_t *ctx = (ucontext_t *)ctx_void;
+
+	segv_err =  ctx->uc_mcontext.gregs[REG_ERR];
 	siglongjmp(jmpbuf, 1);
 }
 
@@ -416,8 +420,11 @@ static int test_vsys_r(void)
 	} else if (!can_read && should_read_vsyscall) {
 		printf("[FAIL]\tWe don't have read access, but we should\n");
 		return 1;
+	} else if (can_read) {
+		printf("[OK]\tWe have read access\n");
 	} else {
-		printf("[OK]\tgot expected result\n");
+		printf("[OK]\tWe do not have read access: #PF(0x%lx)\n",
+		       segv_err);
 	}
 #endif
 
-- 
2.21.0

Re: [PATCH v2 4/8] x86/vsyscall: Document odd SIGSEGV error code for vsyscalls

[Kees Cook]

On Wed, Jun 26, 2019 at 09:45:05PM -0700, Andy Lutomirski wrote:
> Even if vsyscall=none, we report uer page faults on the vsyscall
> page as though the PROT bit in the error code was set.  Add a
> comment explaining why this is probably okay and display the value
> in the test case.
> 
> While we're at it, explain why our behavior is correct with respect
> to PKRU.
> 
> This also modifies the selftest to print the odd error code so that
> you can run the selftest and see that the behavior is odd.
> 
> If anyone really cares about more accurate emulation, we could
> change the behavior.
> 
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  arch/x86/mm/fault.c                         | 7 +++++++
>  tools/testing/selftests/x86/test_vsyscall.c | 9 ++++++++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 288a5462076f..58e4f1f00bbc 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -710,6 +710,10 @@ static void set_signal_archinfo(unsigned long address,
>  	 * To avoid leaking information about the kernel page
>  	 * table layout, pretend that user-mode accesses to
>  	 * kernel addresses are always protection faults.
> +	 *
> +	 * NB: This means that failed vsyscalls with vsyscall=none
> +	 * will have the PROT bit.  This doesn't leak any
> +	 * information and does not appear to cause any problems.
>  	 */
>  	if (address >= TASK_SIZE_MAX)
>  		error_code |= X86_PF_PROT;
> @@ -1375,6 +1379,9 @@ void do_user_addr_fault(struct pt_regs *regs,
>  	 *
>  	 * The vsyscall page does not have a "real" VMA, so do this
>  	 * emulation before we go searching for VMAs.
> +	 *
> +	 * PKRU never rejects instruction fetches, so we don't need
> +	 * to consider the PF_PK bit.
>  	 */
>  	if (is_vsyscall_vaddr(address)) {
>  		if (emulate_vsyscall(hw_error_code, regs, address))
> diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
> index 0b4f1cc2291c..4c9a8d76dba0 100644
> --- a/tools/testing/selftests/x86/test_vsyscall.c
> +++ b/tools/testing/selftests/x86/test_vsyscall.c
> @@ -183,9 +183,13 @@ static inline long sys_getcpu(unsigned * cpu, unsigned * node,
>  }
>  
>  static jmp_buf jmpbuf;
> +static volatile unsigned long segv_err;
>  
>  static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
>  {
> +	ucontext_t *ctx = (ucontext_t *)ctx_void;
> +
> +	segv_err =  ctx->uc_mcontext.gregs[REG_ERR];
>  	siglongjmp(jmpbuf, 1);
>  }
>  
> @@ -416,8 +420,11 @@ static int test_vsys_r(void)
>  	} else if (!can_read && should_read_vsyscall) {
>  		printf("[FAIL]\tWe don't have read access, but we should\n");
>  		return 1;
> +	} else if (can_read) {
> +		printf("[OK]\tWe have read access\n");
>  	} else {
> -		printf("[OK]\tgot expected result\n");
> +		printf("[OK]\tWe do not have read access: #PF(0x%lx)\n",
> +		       segv_err);
>  	}
>  #endif
>  
> -- 
> 2.21.0
> 

-- 
Kees Cook

[tip:x86/entry] x86/vsyscall: Document odd SIGSEGV error code for vsyscalls

[tip-bot for Andy Lutomirski]

Commit-ID:  e0a446ce394a7915f2ffc03f9bb610c5ac4dbbf1
Gitweb:     https://git.kernel.org/tip/e0a446ce394a7915f2ffc03f9bb610c5ac4dbbf1
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 26 Jun 2019 21:45:05 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 28 Jun 2019 00:04:39 +0200

x86/vsyscall: Document odd SIGSEGV error code for vsyscalls

Even if vsyscall=none, user page faults on the vsyscall page are reported
as though the PROT bit in the error code was set.  Add a comment explaining
why this is probably okay and display the value in the test case.

While at it, explain why the behavior is correct with respect to PKRU.

Modify also the selftest to print the odd error code so that there is a
way to demonstrate the odd behaviour.

If anyone really cares about more accurate emulation, the behaviour could
be changed. But that needs a real good justification.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/75c91855fd850649ace162eec5495a1354221aaa.1561610354.git.luto@kernel.org

---
 arch/x86/mm/fault.c                         | 7 +++++++
 tools/testing/selftests/x86/test_vsyscall.c | 9 ++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 288a5462076f..58e4f1f00bbc 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -710,6 +710,10 @@ static void set_signal_archinfo(unsigned long address,
 	 * To avoid leaking information about the kernel page
 	 * table layout, pretend that user-mode accesses to
 	 * kernel addresses are always protection faults.
+	 *
+	 * NB: This means that failed vsyscalls with vsyscall=none
+	 * will have the PROT bit.  This doesn't leak any
+	 * information and does not appear to cause any problems.
 	 */
 	if (address >= TASK_SIZE_MAX)
 		error_code |= X86_PF_PROT;
@@ -1375,6 +1379,9 @@ void do_user_addr_fault(struct pt_regs *regs,
 	 *
 	 * The vsyscall page does not have a "real" VMA, so do this
 	 * emulation before we go searching for VMAs.
+	 *
+	 * PKRU never rejects instruction fetches, so we don't need
+	 * to consider the PF_PK bit.
 	 */
 	if (is_vsyscall_vaddr(address)) {
 		if (emulate_vsyscall(hw_error_code, regs, address))
diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
index 0b4f1cc2291c..4c9a8d76dba0 100644
--- a/tools/testing/selftests/x86/test_vsyscall.c
+++ b/tools/testing/selftests/x86/test_vsyscall.c
@@ -183,9 +183,13 @@ static inline long sys_getcpu(unsigned * cpu, unsigned * node,
 }
 
 static jmp_buf jmpbuf;
+static volatile unsigned long segv_err;
 
 static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
 {
+	ucontext_t *ctx = (ucontext_t *)ctx_void;
+
+	segv_err =  ctx->uc_mcontext.gregs[REG_ERR];
 	siglongjmp(jmpbuf, 1);
 }
 
@@ -416,8 +420,11 @@ static int test_vsys_r(void)
 	} else if (!can_read && should_read_vsyscall) {
 		printf("[FAIL]\tWe don't have read access, but we should\n");
 		return 1;
+	} else if (can_read) {
+		printf("[OK]\tWe have read access\n");
 	} else {
-		printf("[OK]\tgot expected result\n");
+		printf("[OK]\tWe do not have read access: #PF(0x%lx)\n",
+		       segv_err);
 	}
 #endif
 

[PATCH v2 5/8] selftests/x86/vsyscall: Verify that vsyscall=none blocks execution

[Andy Lutomirski]

If vsyscall=none accidentally still allowed vsyscalls, the test
wouldn't fail.  Fix it.

Cc: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 tools/testing/selftests/x86/test_vsyscall.c | 76 ++++++++++++++-------
 1 file changed, 52 insertions(+), 24 deletions(-)

diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
index 4c9a8d76dba0..34a1d35995ef 100644
--- a/tools/testing/selftests/x86/test_vsyscall.c
+++ b/tools/testing/selftests/x86/test_vsyscall.c
@@ -49,21 +49,21 @@ static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
 }
 
 /* vsyscalls and vDSO */
-bool should_read_vsyscall = false;
+bool vsyscall_map_r = false, vsyscall_map_x = false;
 
 typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
-gtod_t vgtod = (gtod_t)VSYS(0xffffffffff600000);
+const gtod_t vgtod = (gtod_t)VSYS(0xffffffffff600000);
 gtod_t vdso_gtod;
 
 typedef int (*vgettime_t)(clockid_t, struct timespec *);
 vgettime_t vdso_gettime;
 
 typedef long (*time_func_t)(time_t *t);
-time_func_t vtime = (time_func_t)VSYS(0xffffffffff600400);
+const time_func_t vtime = (time_func_t)VSYS(0xffffffffff600400);
 time_func_t vdso_time;
 
 typedef long (*getcpu_t)(unsigned *, unsigned *, void *);
-getcpu_t vgetcpu = (getcpu_t)VSYS(0xffffffffff600800);
+const getcpu_t vgetcpu = (getcpu_t)VSYS(0xffffffffff600800);
 getcpu_t vdso_getcpu;
 
 static void init_vdso(void)
@@ -107,7 +107,7 @@ static int init_vsys(void)
 	maps = fopen("/proc/self/maps", "r");
 	if (!maps) {
 		printf("[WARN]\tCould not open /proc/self/maps -- assuming vsyscall is r-x\n");
-		should_read_vsyscall = true;
+		vsyscall_map_r = true;
 		return 0;
 	}
 
@@ -133,12 +133,8 @@ static int init_vsys(void)
 		}
 
 		printf("\tvsyscall permissions are %c-%c\n", r, x);
-		should_read_vsyscall = (r == 'r');
-		if (x != 'x') {
-			vgtod = NULL;
-			vtime = NULL;
-			vgetcpu = NULL;
-		}
+		vsyscall_map_r = (r == 'r');
+		vsyscall_map_x = (x == 'x');
 
 		found = true;
 		break;
@@ -148,10 +144,8 @@ static int init_vsys(void)
 
 	if (!found) {
 		printf("\tno vsyscall map in /proc/self/maps\n");
-		should_read_vsyscall = false;
-		vgtod = NULL;
-		vtime = NULL;
-		vgetcpu = NULL;
+		vsyscall_map_r = false;
+		vsyscall_map_x = false;
 	}
 
 	return nerrs;
@@ -242,7 +236,7 @@ static int test_gtod(void)
 		err(1, "syscall gettimeofday");
 	if (vdso_gtod)
 		ret_vdso = vdso_gtod(&tv_vdso, &tz_vdso);
-	if (vgtod)
+	if (vsyscall_map_x)
 		ret_vsys = vgtod(&tv_vsys, &tz_vsys);
 	if (sys_gtod(&tv_sys2, &tz_sys) != 0)
 		err(1, "syscall gettimeofday");
@@ -256,7 +250,7 @@ static int test_gtod(void)
 		}
 	}
 
-	if (vgtod) {
+	if (vsyscall_map_x) {
 		if (ret_vsys == 0) {
 			nerrs += check_gtod(&tv_sys1, &tv_sys2, &tz_sys, "vsyscall", &tv_vsys, &tz_vsys);
 		} else {
@@ -277,7 +271,7 @@ static int test_time(void) {
 	t_sys1 = sys_time(&t2_sys1);
 	if (vdso_time)
 		t_vdso = vdso_time(&t2_vdso);
-	if (vtime)
+	if (vsyscall_map_x)
 		t_vsys = vtime(&t2_vsys);
 	t_sys2 = sys_time(&t2_sys2);
 	if (t_sys1 < 0 || t_sys1 != t2_sys1 || t_sys2 < 0 || t_sys2 != t2_sys2) {
@@ -298,7 +292,7 @@ static int test_time(void) {
 		}
 	}
 
-	if (vtime) {
+	if (vsyscall_map_x) {
 		if (t_vsys < 0 || t_vsys != t2_vsys) {
 			printf("[FAIL]\tvsyscall failed (ret:%ld output:%ld)\n", t_vsys, t2_vsys);
 			nerrs++;
@@ -334,7 +328,7 @@ static int test_getcpu(int cpu)
 	ret_sys = sys_getcpu(&cpu_sys, &node_sys, 0);
 	if (vdso_getcpu)
 		ret_vdso = vdso_getcpu(&cpu_vdso, &node_vdso, 0);
-	if (vgetcpu)
+	if (vsyscall_map_x)
 		ret_vsys = vgetcpu(&cpu_vsys, &node_vsys, 0);
 
 	if (ret_sys == 0) {
@@ -373,7 +367,7 @@ static int test_getcpu(int cpu)
 		}
 	}
 
-	if (vgetcpu) {
+	if (vsyscall_map_x) {
 		if (ret_vsys) {
 			printf("[FAIL]\tvsyscall getcpu() failed\n");
 			nerrs++;
@@ -414,10 +408,10 @@ static int test_vsys_r(void)
 		can_read = false;
 	}
 
-	if (can_read && !should_read_vsyscall) {
+	if (can_read && !vsyscall_map_r) {
 		printf("[FAIL]\tWe have read access, but we shouldn't\n");
 		return 1;
-	} else if (!can_read && should_read_vsyscall) {
+	} else if (!can_read && vsyscall_map_r) {
 		printf("[FAIL]\tWe don't have read access, but we should\n");
 		return 1;
 	} else if (can_read) {
@@ -431,6 +425,39 @@ static int test_vsys_r(void)
 	return 0;
 }
 
+static int test_vsys_x(void)
+{
+#ifdef __x86_64__
+	if (vsyscall_map_x) {
+		/* We already tested this adequately. */
+		return 0;
+	}
+
+	printf("[RUN]\tMake sure that vsyscalls really page fault\n");
+
+	bool can_exec;
+	if (sigsetjmp(jmpbuf, 1) == 0) {
+		vgtod(NULL, NULL);
+		can_exec = true;
+	} else {
+		can_exec = false;
+	}
+
+	if (can_exec) {
+		printf("[FAIL]\tExecuting the vsyscall did not page fault\n");
+		return 1;
+	} else if (segv_err & (1 << 4)) { /* INSTR */
+		printf("[OK]\tExecuting the vsyscall page failed: #PF(0x%lx)\n",
+		       segv_err);
+	} else {
+		printf("[FAILT]\tExecution failed with the wrong error: #PF(0x%lx)\n",
+		       segv_err);
+		return 1;
+	}
+#endif
+
+	return 0;
+}
 
 #ifdef __x86_64__
 #define X86_EFLAGS_TF (1UL << 8)
@@ -462,7 +489,7 @@ static int test_emulation(void)
 	time_t tmp;
 	bool is_native;
 
-	if (!vtime)
+	if (!vsyscall_map_x)
 		return 0;
 
 	printf("[RUN]\tchecking that vsyscalls are emulated\n");
@@ -504,6 +531,7 @@ int main(int argc, char **argv)
 
 	sethandler(SIGSEGV, sigsegv, 0);
 	nerrs += test_vsys_r();
+	nerrs += test_vsys_x();
 
 #ifdef __x86_64__
 	nerrs += test_emulation();
-- 
2.21.0

Re: [PATCH v2 5/8] selftests/x86/vsyscall: Verify that vsyscall=none blocks execution

[Kees Cook]

On Wed, Jun 26, 2019 at 09:45:06PM -0700, Andy Lutomirski wrote:
> If vsyscall=none accidentally still allowed vsyscalls, the test
> wouldn't fail.  Fix it.
> 
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  tools/testing/selftests/x86/test_vsyscall.c | 76 ++++++++++++++-------
>  1 file changed, 52 insertions(+), 24 deletions(-)
> 
> diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
> index 4c9a8d76dba0..34a1d35995ef 100644
> --- a/tools/testing/selftests/x86/test_vsyscall.c
> +++ b/tools/testing/selftests/x86/test_vsyscall.c
> @@ -49,21 +49,21 @@ static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
>  }
>  
>  /* vsyscalls and vDSO */
> -bool should_read_vsyscall = false;
> +bool vsyscall_map_r = false, vsyscall_map_x = false;
>  
>  typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
> -gtod_t vgtod = (gtod_t)VSYS(0xffffffffff600000);
> +const gtod_t vgtod = (gtod_t)VSYS(0xffffffffff600000);
>  gtod_t vdso_gtod;
>  
>  typedef int (*vgettime_t)(clockid_t, struct timespec *);
>  vgettime_t vdso_gettime;
>  
>  typedef long (*time_func_t)(time_t *t);
> -time_func_t vtime = (time_func_t)VSYS(0xffffffffff600400);
> +const time_func_t vtime = (time_func_t)VSYS(0xffffffffff600400);
>  time_func_t vdso_time;
>  
>  typedef long (*getcpu_t)(unsigned *, unsigned *, void *);
> -getcpu_t vgetcpu = (getcpu_t)VSYS(0xffffffffff600800);
> +const getcpu_t vgetcpu = (getcpu_t)VSYS(0xffffffffff600800);
>  getcpu_t vdso_getcpu;
>  
>  static void init_vdso(void)
> @@ -107,7 +107,7 @@ static int init_vsys(void)
>  	maps = fopen("/proc/self/maps", "r");
>  	if (!maps) {
>  		printf("[WARN]\tCould not open /proc/self/maps -- assuming vsyscall is r-x\n");
> -		should_read_vsyscall = true;
> +		vsyscall_map_r = true;
>  		return 0;
>  	}
>  
> @@ -133,12 +133,8 @@ static int init_vsys(void)
>  		}
>  
>  		printf("\tvsyscall permissions are %c-%c\n", r, x);
> -		should_read_vsyscall = (r == 'r');
> -		if (x != 'x') {
> -			vgtod = NULL;
> -			vtime = NULL;
> -			vgetcpu = NULL;
> -		}
> +		vsyscall_map_r = (r == 'r');
> +		vsyscall_map_x = (x == 'x');
>  
>  		found = true;
>  		break;
> @@ -148,10 +144,8 @@ static int init_vsys(void)
>  
>  	if (!found) {
>  		printf("\tno vsyscall map in /proc/self/maps\n");
> -		should_read_vsyscall = false;
> -		vgtod = NULL;
> -		vtime = NULL;
> -		vgetcpu = NULL;
> +		vsyscall_map_r = false;
> +		vsyscall_map_x = false;
>  	}
>  
>  	return nerrs;
> @@ -242,7 +236,7 @@ static int test_gtod(void)
>  		err(1, "syscall gettimeofday");
>  	if (vdso_gtod)
>  		ret_vdso = vdso_gtod(&tv_vdso, &tz_vdso);
> -	if (vgtod)
> +	if (vsyscall_map_x)
>  		ret_vsys = vgtod(&tv_vsys, &tz_vsys);
>  	if (sys_gtod(&tv_sys2, &tz_sys) != 0)
>  		err(1, "syscall gettimeofday");
> @@ -256,7 +250,7 @@ static int test_gtod(void)
>  		}
>  	}
>  
> -	if (vgtod) {
> +	if (vsyscall_map_x) {
>  		if (ret_vsys == 0) {
>  			nerrs += check_gtod(&tv_sys1, &tv_sys2, &tz_sys, "vsyscall", &tv_vsys, &tz_vsys);
>  		} else {
> @@ -277,7 +271,7 @@ static int test_time(void) {
>  	t_sys1 = sys_time(&t2_sys1);
>  	if (vdso_time)
>  		t_vdso = vdso_time(&t2_vdso);
> -	if (vtime)
> +	if (vsyscall_map_x)
>  		t_vsys = vtime(&t2_vsys);
>  	t_sys2 = sys_time(&t2_sys2);
>  	if (t_sys1 < 0 || t_sys1 != t2_sys1 || t_sys2 < 0 || t_sys2 != t2_sys2) {
> @@ -298,7 +292,7 @@ static int test_time(void) {
>  		}
>  	}
>  
> -	if (vtime) {
> +	if (vsyscall_map_x) {
>  		if (t_vsys < 0 || t_vsys != t2_vsys) {
>  			printf("[FAIL]\tvsyscall failed (ret:%ld output:%ld)\n", t_vsys, t2_vsys);
>  			nerrs++;
> @@ -334,7 +328,7 @@ static int test_getcpu(int cpu)
>  	ret_sys = sys_getcpu(&cpu_sys, &node_sys, 0);
>  	if (vdso_getcpu)
>  		ret_vdso = vdso_getcpu(&cpu_vdso, &node_vdso, 0);
> -	if (vgetcpu)
> +	if (vsyscall_map_x)
>  		ret_vsys = vgetcpu(&cpu_vsys, &node_vsys, 0);
>  
>  	if (ret_sys == 0) {
> @@ -373,7 +367,7 @@ static int test_getcpu(int cpu)
>  		}
>  	}
>  
> -	if (vgetcpu) {
> +	if (vsyscall_map_x) {
>  		if (ret_vsys) {
>  			printf("[FAIL]\tvsyscall getcpu() failed\n");
>  			nerrs++;
> @@ -414,10 +408,10 @@ static int test_vsys_r(void)
>  		can_read = false;
>  	}
>  
> -	if (can_read && !should_read_vsyscall) {
> +	if (can_read && !vsyscall_map_r) {
>  		printf("[FAIL]\tWe have read access, but we shouldn't\n");
>  		return 1;
> -	} else if (!can_read && should_read_vsyscall) {
> +	} else if (!can_read && vsyscall_map_r) {
>  		printf("[FAIL]\tWe don't have read access, but we should\n");
>  		return 1;
>  	} else if (can_read) {
> @@ -431,6 +425,39 @@ static int test_vsys_r(void)
>  	return 0;
>  }
>  
> +static int test_vsys_x(void)
> +{
> +#ifdef __x86_64__
> +	if (vsyscall_map_x) {
> +		/* We already tested this adequately. */
> +		return 0;
> +	}
> +
> +	printf("[RUN]\tMake sure that vsyscalls really page fault\n");
> +
> +	bool can_exec;
> +	if (sigsetjmp(jmpbuf, 1) == 0) {
> +		vgtod(NULL, NULL);
> +		can_exec = true;
> +	} else {
> +		can_exec = false;
> +	}
> +
> +	if (can_exec) {
> +		printf("[FAIL]\tExecuting the vsyscall did not page fault\n");
> +		return 1;
> +	} else if (segv_err & (1 << 4)) { /* INSTR */
> +		printf("[OK]\tExecuting the vsyscall page failed: #PF(0x%lx)\n",
> +		       segv_err);
> +	} else {
> +		printf("[FAILT]\tExecution failed with the wrong error: #PF(0x%lx)\n",
> +		       segv_err);
> +		return 1;
> +	}
> +#endif
> +
> +	return 0;
> +}
>  
>  #ifdef __x86_64__
>  #define X86_EFLAGS_TF (1UL << 8)
> @@ -462,7 +489,7 @@ static int test_emulation(void)
>  	time_t tmp;
>  	bool is_native;
>  
> -	if (!vtime)
> +	if (!vsyscall_map_x)
>  		return 0;
>  
>  	printf("[RUN]\tchecking that vsyscalls are emulated\n");
> @@ -504,6 +531,7 @@ int main(int argc, char **argv)
>  
>  	sethandler(SIGSEGV, sigsegv, 0);
>  	nerrs += test_vsys_r();
> +	nerrs += test_vsys_x();
>  
>  #ifdef __x86_64__
>  	nerrs += test_emulation();
> -- 
> 2.21.0
> 

-- 
Kees Cook

[tip:x86/entry] selftests/x86/vsyscall: Verify that vsyscall=none blocks execution

[tip-bot for Andy Lutomirski]

Commit-ID:  b0386979867168575118501104f3d135067eab4f
Gitweb:     https://git.kernel.org/tip/b0386979867168575118501104f3d135067eab4f
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 26 Jun 2019 21:45:06 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 28 Jun 2019 00:04:39 +0200

selftests/x86/vsyscall: Verify that vsyscall=none blocks execution

If vsyscall=none accidentally still allowed vsyscalls, the test wouldn't
fail.  Fix it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/b413397c804265f8865f3e70b14b09485ea7c314.1561610354.git.luto@kernel.org

---
 tools/testing/selftests/x86/test_vsyscall.c | 76 ++++++++++++++++++++---------
 1 file changed, 52 insertions(+), 24 deletions(-)

diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
index 4c9a8d76dba0..34a1d35995ef 100644
--- a/tools/testing/selftests/x86/test_vsyscall.c
+++ b/tools/testing/selftests/x86/test_vsyscall.c
@@ -49,21 +49,21 @@ static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
 }
 
 /* vsyscalls and vDSO */
-bool should_read_vsyscall = false;
+bool vsyscall_map_r = false, vsyscall_map_x = false;
 
 typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
-gtod_t vgtod = (gtod_t)VSYS(0xffffffffff600000);
+const gtod_t vgtod = (gtod_t)VSYS(0xffffffffff600000);
 gtod_t vdso_gtod;
 
 typedef int (*vgettime_t)(clockid_t, struct timespec *);
 vgettime_t vdso_gettime;
 
 typedef long (*time_func_t)(time_t *t);
-time_func_t vtime = (time_func_t)VSYS(0xffffffffff600400);
+const time_func_t vtime = (time_func_t)VSYS(0xffffffffff600400);
 time_func_t vdso_time;
 
 typedef long (*getcpu_t)(unsigned *, unsigned *, void *);
-getcpu_t vgetcpu = (getcpu_t)VSYS(0xffffffffff600800);
+const getcpu_t vgetcpu = (getcpu_t)VSYS(0xffffffffff600800);
 getcpu_t vdso_getcpu;
 
 static void init_vdso(void)
@@ -107,7 +107,7 @@ static int init_vsys(void)
 	maps = fopen("/proc/self/maps", "r");
 	if (!maps) {
 		printf("[WARN]\tCould not open /proc/self/maps -- assuming vsyscall is r-x\n");
-		should_read_vsyscall = true;
+		vsyscall_map_r = true;
 		return 0;
 	}
 
@@ -133,12 +133,8 @@ static int init_vsys(void)
 		}
 
 		printf("\tvsyscall permissions are %c-%c\n", r, x);
-		should_read_vsyscall = (r == 'r');
-		if (x != 'x') {
-			vgtod = NULL;
-			vtime = NULL;
-			vgetcpu = NULL;
-		}
+		vsyscall_map_r = (r == 'r');
+		vsyscall_map_x = (x == 'x');
 
 		found = true;
 		break;
@@ -148,10 +144,8 @@ static int init_vsys(void)
 
 	if (!found) {
 		printf("\tno vsyscall map in /proc/self/maps\n");
-		should_read_vsyscall = false;
-		vgtod = NULL;
-		vtime = NULL;
-		vgetcpu = NULL;
+		vsyscall_map_r = false;
+		vsyscall_map_x = false;
 	}
 
 	return nerrs;
@@ -242,7 +236,7 @@ static int test_gtod(void)
 		err(1, "syscall gettimeofday");
 	if (vdso_gtod)
 		ret_vdso = vdso_gtod(&tv_vdso, &tz_vdso);
-	if (vgtod)
+	if (vsyscall_map_x)
 		ret_vsys = vgtod(&tv_vsys, &tz_vsys);
 	if (sys_gtod(&tv_sys2, &tz_sys) != 0)
 		err(1, "syscall gettimeofday");
@@ -256,7 +250,7 @@ static int test_gtod(void)
 		}
 	}
 
-	if (vgtod) {
+	if (vsyscall_map_x) {
 		if (ret_vsys == 0) {
 			nerrs += check_gtod(&tv_sys1, &tv_sys2, &tz_sys, "vsyscall", &tv_vsys, &tz_vsys);
 		} else {
@@ -277,7 +271,7 @@ static int test_time(void) {
 	t_sys1 = sys_time(&t2_sys1);
 	if (vdso_time)
 		t_vdso = vdso_time(&t2_vdso);
-	if (vtime)
+	if (vsyscall_map_x)
 		t_vsys = vtime(&t2_vsys);
 	t_sys2 = sys_time(&t2_sys2);
 	if (t_sys1 < 0 || t_sys1 != t2_sys1 || t_sys2 < 0 || t_sys2 != t2_sys2) {
@@ -298,7 +292,7 @@ static int test_time(void) {
 		}
 	}
 
-	if (vtime) {
+	if (vsyscall_map_x) {
 		if (t_vsys < 0 || t_vsys != t2_vsys) {
 			printf("[FAIL]\tvsyscall failed (ret:%ld output:%ld)\n", t_vsys, t2_vsys);
 			nerrs++;
@@ -334,7 +328,7 @@ static int test_getcpu(int cpu)
 	ret_sys = sys_getcpu(&cpu_sys, &node_sys, 0);
 	if (vdso_getcpu)
 		ret_vdso = vdso_getcpu(&cpu_vdso, &node_vdso, 0);
-	if (vgetcpu)
+	if (vsyscall_map_x)
 		ret_vsys = vgetcpu(&cpu_vsys, &node_vsys, 0);
 
 	if (ret_sys == 0) {
@@ -373,7 +367,7 @@ static int test_getcpu(int cpu)
 		}
 	}
 
-	if (vgetcpu) {
+	if (vsyscall_map_x) {
 		if (ret_vsys) {
 			printf("[FAIL]\tvsyscall getcpu() failed\n");
 			nerrs++;
@@ -414,10 +408,10 @@ static int test_vsys_r(void)
 		can_read = false;
 	}
 
-	if (can_read && !should_read_vsyscall) {
+	if (can_read && !vsyscall_map_r) {
 		printf("[FAIL]\tWe have read access, but we shouldn't\n");
 		return 1;
-	} else if (!can_read && should_read_vsyscall) {
+	} else if (!can_read && vsyscall_map_r) {
 		printf("[FAIL]\tWe don't have read access, but we should\n");
 		return 1;
 	} else if (can_read) {
@@ -431,6 +425,39 @@ static int test_vsys_r(void)
 	return 0;
 }
 
+static int test_vsys_x(void)
+{
+#ifdef __x86_64__
+	if (vsyscall_map_x) {
+		/* We already tested this adequately. */
+		return 0;
+	}
+
+	printf("[RUN]\tMake sure that vsyscalls really page fault\n");
+
+	bool can_exec;
+	if (sigsetjmp(jmpbuf, 1) == 0) {
+		vgtod(NULL, NULL);
+		can_exec = true;
+	} else {
+		can_exec = false;
+	}
+
+	if (can_exec) {
+		printf("[FAIL]\tExecuting the vsyscall did not page fault\n");
+		return 1;
+	} else if (segv_err & (1 << 4)) { /* INSTR */
+		printf("[OK]\tExecuting the vsyscall page failed: #PF(0x%lx)\n",
+		       segv_err);
+	} else {
+		printf("[FAILT]\tExecution failed with the wrong error: #PF(0x%lx)\n",
+		       segv_err);
+		return 1;
+	}
+#endif
+
+	return 0;
+}
 
 #ifdef __x86_64__
 #define X86_EFLAGS_TF (1UL << 8)
@@ -462,7 +489,7 @@ static int test_emulation(void)
 	time_t tmp;
 	bool is_native;
 
-	if (!vtime)
+	if (!vsyscall_map_x)
 		return 0;
 
 	printf("[RUN]\tchecking that vsyscalls are emulated\n");
@@ -504,6 +531,7 @@ int main(int argc, char **argv)
 
 	sethandler(SIGSEGV, sigsegv, 0);
 	nerrs += test_vsys_r();
+	nerrs += test_vsys_x();
 
 #ifdef __x86_64__
 	nerrs += test_emulation();

[PATCH v2 6/8] x86/vsyscall: Change the default vsyscall mode to xonly

[Andy Lutomirski]

The use case for full emulation over xonly is very esoteric.  Let's
change the default to the safer xonly mode.

Cc: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0182d2c67590..32028edc1b0e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2285,7 +2285,7 @@ config COMPAT_VDSO
 choice
 	prompt "vsyscall table for legacy applications"
 	depends on X86_64
-	default LEGACY_VSYSCALL_EMULATE
+	default LEGACY_VSYSCALL_XONLY
 	help
 	  Legacy user code that does not know how to find the vDSO expects
 	  to be able to issue three syscalls by calling fixed addresses in
-- 
2.21.0

Re: [PATCH v2 6/8] x86/vsyscall: Change the default vsyscall mode to xonly

[Kees Cook]

On Wed, Jun 26, 2019 at 09:45:07PM -0700, Andy Lutomirski wrote:
> The use case for full emulation over xonly is very esoteric.  Let's
> change the default to the safer xonly mode.
> 
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

I still think it'd be valuable to describe any known esoteric cases
here, but regardless:

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  arch/x86/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 0182d2c67590..32028edc1b0e 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2285,7 +2285,7 @@ config COMPAT_VDSO
>  choice
>  	prompt "vsyscall table for legacy applications"
>  	depends on X86_64
> -	default LEGACY_VSYSCALL_EMULATE
> +	default LEGACY_VSYSCALL_XONLY
>  	help
>  	  Legacy user code that does not know how to find the vDSO expects
>  	  to be able to issue three syscalls by calling fixed addresses in
> -- 
> 2.21.0
> 

-- 
Kees Cook

[tip:x86/entry] x86/vsyscall: Change the default vsyscall mode to xonly

[tip-bot for Andy Lutomirski]

Commit-ID:  625b7b7f79c66626fb2b7687fc1a58309a57edd5
Gitweb:     https://git.kernel.org/tip/625b7b7f79c66626fb2b7687fc1a58309a57edd5
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 26 Jun 2019 21:45:07 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 28 Jun 2019 00:04:39 +0200

x86/vsyscall: Change the default vsyscall mode to xonly

The use case for full emulation over xonly is very esoteric, e.g. magic
instrumentation tools.

Change the default to the safer xonly mode.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/30539f8072d2376b9c9efcc07e6ed0d6bf20e882.1561610354.git.luto@kernel.org

---
 arch/x86/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0182d2c67590..32028edc1b0e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2285,7 +2285,7 @@ config COMPAT_VDSO
 choice
 	prompt "vsyscall table for legacy applications"
 	depends on X86_64
-	default LEGACY_VSYSCALL_EMULATE
+	default LEGACY_VSYSCALL_XONLY
 	help
 	  Legacy user code that does not know how to find the vDSO expects
 	  to be able to issue three syscalls by calling fixed addresses in

[PATCH v2 7/8] x86/vsyscall: Add __ro_after_init to global variables

[Andy Lutomirski]

The vDSO is only configurable by command-line options, so make its
global variables __ro_after_init.  This seems highly unlikely to
ever stop an exploit, but I think it's nice anyway.

Cc: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/entry/vsyscall/vsyscall_64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index 9c58ab807aeb..07003f3f1bfc 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -42,7 +42,7 @@
 #define CREATE_TRACE_POINTS
 #include "vsyscall_trace.h"
 
-static enum { EMULATE, XONLY, NONE } vsyscall_mode =
+static enum { EMULATE, XONLY, NONE } vsyscall_mode __ro_after_init =
 #ifdef CONFIG_LEGACY_VSYSCALL_NONE
 	NONE;
 #elif defined(CONFIG_LEGACY_VSYSCALL_XONLY)
@@ -305,7 +305,7 @@ static const char *gate_vma_name(struct vm_area_struct *vma)
 static const struct vm_operations_struct gate_vma_ops = {
 	.name = gate_vma_name,
 };
-static struct vm_area_struct gate_vma = {
+static struct vm_area_struct gate_vma __ro_after_init = {
 	.vm_start	= VSYSCALL_ADDR,
 	.vm_end		= VSYSCALL_ADDR + PAGE_SIZE,
 	.vm_page_prot	= PAGE_READONLY_EXEC,
-- 
2.21.0

Re: [PATCH v2 7/8] x86/vsyscall: Add __ro_after_init to global variables

[Kees Cook]

On Wed, Jun 26, 2019 at 09:45:08PM -0700, Andy Lutomirski wrote:
> The vDSO is only configurable by command-line options, so make its
> global variables __ro_after_init.  This seems highly unlikely to
> ever stop an exploit, but I think it's nice anyway.
> 
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  arch/x86/entry/vsyscall/vsyscall_64.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
> index 9c58ab807aeb..07003f3f1bfc 100644
> --- a/arch/x86/entry/vsyscall/vsyscall_64.c
> +++ b/arch/x86/entry/vsyscall/vsyscall_64.c
> @@ -42,7 +42,7 @@
>  #define CREATE_TRACE_POINTS
>  #include "vsyscall_trace.h"
>  
> -static enum { EMULATE, XONLY, NONE } vsyscall_mode =
> +static enum { EMULATE, XONLY, NONE } vsyscall_mode __ro_after_init =
>  #ifdef CONFIG_LEGACY_VSYSCALL_NONE
>  	NONE;
>  #elif defined(CONFIG_LEGACY_VSYSCALL_XONLY)
> @@ -305,7 +305,7 @@ static const char *gate_vma_name(struct vm_area_struct *vma)
>  static const struct vm_operations_struct gate_vma_ops = {
>  	.name = gate_vma_name,
>  };
> -static struct vm_area_struct gate_vma = {
> +static struct vm_area_struct gate_vma __ro_after_init = {
>  	.vm_start	= VSYSCALL_ADDR,
>  	.vm_end		= VSYSCALL_ADDR + PAGE_SIZE,
>  	.vm_page_prot	= PAGE_READONLY_EXEC,
> -- 
> 2.21.0
> 

-- 
Kees Cook

[tip:x86/entry] x86/vsyscall: Add __ro_after_init to global variables

[tip-bot for Andy Lutomirski]

Commit-ID:  441cedab2dfca18fe4983cbc795de04536ed421e
Gitweb:     https://git.kernel.org/tip/441cedab2dfca18fe4983cbc795de04536ed421e
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 26 Jun 2019 21:45:08 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 28 Jun 2019 00:04:40 +0200

x86/vsyscall: Add __ro_after_init to global variables

The vDSO is only configurable by command-line options, so make its
global variables __ro_after_init.  This seems highly unlikely to
ever stop an exploit, but it's nicer anyway.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/a386925835e49d319e70c4d7404b1f6c3c2e3702.1561610354.git.luto@kernel.org

---
 arch/x86/entry/vsyscall/vsyscall_64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index 9c58ab807aeb..07003f3f1bfc 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -42,7 +42,7 @@
 #define CREATE_TRACE_POINTS
 #include "vsyscall_trace.h"
 
-static enum { EMULATE, XONLY, NONE } vsyscall_mode =
+static enum { EMULATE, XONLY, NONE } vsyscall_mode __ro_after_init =
 #ifdef CONFIG_LEGACY_VSYSCALL_NONE
 	NONE;
 #elif defined(CONFIG_LEGACY_VSYSCALL_XONLY)
@@ -305,7 +305,7 @@ static const char *gate_vma_name(struct vm_area_struct *vma)
 static const struct vm_operations_struct gate_vma_ops = {
 	.name = gate_vma_name,
 };
-static struct vm_area_struct gate_vma = {
+static struct vm_area_struct gate_vma __ro_after_init = {
 	.vm_start	= VSYSCALL_ADDR,
 	.vm_end		= VSYSCALL_ADDR + PAGE_SIZE,
 	.vm_page_prot	= PAGE_READONLY_EXEC,

[PATCH v2 8/8] selftests/x86: Add a test for process_vm_readv() on the vsyscall page

[Andy Lutomirski]

get_gate_page() is a piece of somewhat alarming code to make
get_user_pages() work on the vsyscall page.  Test it via
process_vm_readv().

Cc: Kees Cook <keescook@chromium.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 tools/testing/selftests/x86/test_vsyscall.c | 35 +++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
index 34a1d35995ef..4602326b8f5b 100644
--- a/tools/testing/selftests/x86/test_vsyscall.c
+++ b/tools/testing/selftests/x86/test_vsyscall.c
@@ -18,6 +18,7 @@
 #include <sched.h>
 #include <stdbool.h>
 #include <setjmp.h>
+#include <sys/uio.h>
 
 #ifdef __x86_64__
 # define VSYS(x) (x)
@@ -459,6 +460,38 @@ static int test_vsys_x(void)
 	return 0;
 }
 
+static int test_process_vm_readv(void)
+{
+#ifdef __x86_64__
+	char buf[4096];
+	struct iovec local, remote;
+	int ret;
+
+	printf("[RUN]\tprocess_vm_readv() from vsyscall page\n");
+
+	local.iov_base = buf;
+	local.iov_len = 4096;
+	remote.iov_base = (void *)0xffffffffff600000;
+	remote.iov_len = 4096;
+	ret = process_vm_readv(getpid(), &local, 1, &remote, 1, 0);
+	if (ret != 4096) {
+		printf("[OK]\tprocess_vm_readv() failed (ret = %d, errno = %d)\n", ret, errno);
+		return 0;
+	}
+
+	if (vsyscall_map_r) {
+		if (!memcmp(buf, (const void *)0xffffffffff600000, 4096)) {
+			printf("[OK]\tIt worked and read correct data\n");
+		} else {
+			printf("[FAIL]\tIt worked but returned incorrect data\n");
+			return 1;
+		}
+	}
+#endif
+
+	return 0;
+}
+
 #ifdef __x86_64__
 #define X86_EFLAGS_TF (1UL << 8)
 static volatile sig_atomic_t num_vsyscall_traps;
@@ -533,6 +566,8 @@ int main(int argc, char **argv)
 	nerrs += test_vsys_r();
 	nerrs += test_vsys_x();
 
+	nerrs += test_process_vm_readv();
+
 #ifdef __x86_64__
 	nerrs += test_emulation();
 #endif
-- 
2.21.0

Re: [PATCH v2 8/8] selftests/x86: Add a test for process_vm_readv() on the vsyscall page

[Kees Cook]

On Wed, Jun 26, 2019 at 09:45:09PM -0700, Andy Lutomirski wrote:
> get_gate_page() is a piece of somewhat alarming code to make
> get_user_pages() work on the vsyscall page.  Test it via
> process_vm_readv().
> 
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  tools/testing/selftests/x86/test_vsyscall.c | 35 +++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
> index 34a1d35995ef..4602326b8f5b 100644
> --- a/tools/testing/selftests/x86/test_vsyscall.c
> +++ b/tools/testing/selftests/x86/test_vsyscall.c
> @@ -18,6 +18,7 @@
>  #include <sched.h>
>  #include <stdbool.h>
>  #include <setjmp.h>
> +#include <sys/uio.h>
>  
>  #ifdef __x86_64__
>  # define VSYS(x) (x)
> @@ -459,6 +460,38 @@ static int test_vsys_x(void)
>  	return 0;
>  }
>  
> +static int test_process_vm_readv(void)
> +{
> +#ifdef __x86_64__
> +	char buf[4096];
> +	struct iovec local, remote;
> +	int ret;
> +
> +	printf("[RUN]\tprocess_vm_readv() from vsyscall page\n");
> +
> +	local.iov_base = buf;
> +	local.iov_len = 4096;
> +	remote.iov_base = (void *)0xffffffffff600000;
> +	remote.iov_len = 4096;
> +	ret = process_vm_readv(getpid(), &local, 1, &remote, 1, 0);
> +	if (ret != 4096) {
> +		printf("[OK]\tprocess_vm_readv() failed (ret = %d, errno = %d)\n", ret, errno);
> +		return 0;
> +	}
> +
> +	if (vsyscall_map_r) {
> +		if (!memcmp(buf, (const void *)0xffffffffff600000, 4096)) {
> +			printf("[OK]\tIt worked and read correct data\n");
> +		} else {
> +			printf("[FAIL]\tIt worked but returned incorrect data\n");
> +			return 1;
> +		}
> +	}
> +#endif
> +
> +	return 0;
> +}
> +
>  #ifdef __x86_64__
>  #define X86_EFLAGS_TF (1UL << 8)
>  static volatile sig_atomic_t num_vsyscall_traps;
> @@ -533,6 +566,8 @@ int main(int argc, char **argv)
>  	nerrs += test_vsys_r();
>  	nerrs += test_vsys_x();
>  
> +	nerrs += test_process_vm_readv();
> +
>  #ifdef __x86_64__
>  	nerrs += test_emulation();
>  #endif
> -- 
> 2.21.0
> 

-- 
Kees Cook

[tip:x86/entry] selftests/x86: Add a test for process_vm_readv() on the vsyscall page

[tip-bot for Andy Lutomirski]

Commit-ID:  7f0a5e0755832301e7b010eab46fb715c483ba60
Gitweb:     https://git.kernel.org/tip/7f0a5e0755832301e7b010eab46fb715c483ba60
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 26 Jun 2019 21:45:09 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 28 Jun 2019 00:04:40 +0200

selftests/x86: Add a test for process_vm_readv() on the vsyscall page

get_gate_page() is a piece of somewhat alarming code to make
get_user_pages() work on the vsyscall page.  Test it via
process_vm_readv().

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/0fe34229a9330e8f9de9765967939cc4f1cf26b1.1561610354.git.luto@kernel.org

---
 tools/testing/selftests/x86/test_vsyscall.c | 35 +++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/tools/testing/selftests/x86/test_vsyscall.c b/tools/testing/selftests/x86/test_vsyscall.c
index 34a1d35995ef..4602326b8f5b 100644
--- a/tools/testing/selftests/x86/test_vsyscall.c
+++ b/tools/testing/selftests/x86/test_vsyscall.c
@@ -18,6 +18,7 @@
 #include <sched.h>
 #include <stdbool.h>
 #include <setjmp.h>
+#include <sys/uio.h>
 
 #ifdef __x86_64__
 # define VSYS(x) (x)
@@ -459,6 +460,38 @@ static int test_vsys_x(void)
 	return 0;
 }
 
+static int test_process_vm_readv(void)
+{
+#ifdef __x86_64__
+	char buf[4096];
+	struct iovec local, remote;
+	int ret;
+
+	printf("[RUN]\tprocess_vm_readv() from vsyscall page\n");
+
+	local.iov_base = buf;
+	local.iov_len = 4096;
+	remote.iov_base = (void *)0xffffffffff600000;
+	remote.iov_len = 4096;
+	ret = process_vm_readv(getpid(), &local, 1, &remote, 1, 0);
+	if (ret != 4096) {
+		printf("[OK]\tprocess_vm_readv() failed (ret = %d, errno = %d)\n", ret, errno);
+		return 0;
+	}
+
+	if (vsyscall_map_r) {
+		if (!memcmp(buf, (const void *)0xffffffffff600000, 4096)) {
+			printf("[OK]\tIt worked and read correct data\n");
+		} else {
+			printf("[FAIL]\tIt worked but returned incorrect data\n");
+			return 1;
+		}
+	}
+#endif
+
+	return 0;
+}
+
 #ifdef __x86_64__
 #define X86_EFLAGS_TF (1UL << 8)
 static volatile sig_atomic_t num_vsyscall_traps;
@@ -533,6 +566,8 @@ int main(int argc, char **argv)
 	nerrs += test_vsys_r();
 	nerrs += test_vsys_x();
 
+	nerrs += test_process_vm_readv();
+
 #ifdef __x86_64__
 	nerrs += test_emulation();
 #endif