[PATCH v3] selftests/x86: Support Atom for syscall_arg_fault test

[PATCH v3] selftests/x86: Support Atom for syscall_arg_fault test

[Tong Bo]

Atom-based CPUs trigger stack fault when invoke 32-bit SYSENTER instruction
with invalid register values. So we also need SIGBUS handling in this case.

Following is assembly when the fault exception happens.

(gdb) disassemble $eip
Dump of assembler code for function __kernel_vsyscall:
   0xf7fd8fe0 <+0>:     push   %ecx
   0xf7fd8fe1 <+1>:     push   %edx
   0xf7fd8fe2 <+2>:     push   %ebp
   0xf7fd8fe3 <+3>:     mov    %esp,%ebp
   0xf7fd8fe5 <+5>:     sysenter
   0xf7fd8fe7 <+7>:     int    $0x80
=> 0xf7fd8fe9 <+9>:     pop    %ebp
   0xf7fd8fea <+10>:    pop    %edx
   0xf7fd8feb <+11>:    pop    %ecx
   0xf7fd8fec <+12>:    ret
End of assembler dump.

According to Intel SDM, this could also be a Stack Segment Fault(#SS, 12),
except a normal Page Fault(#PF, 14). Especially, in section 6.9 of Vol.3A,
both stack and page faults are within the 10th(lowest priority) class, and
as it said, "exceptions within each class are implementation-dependent and
may vary from processor to processor". It's expected for processors like
Intel Atom to trigger stack fault(SIGBUS), while we get page fault(SIGSEGV)
from common Core processors.

Signed-off-by: Tong Bo <bo.tong@intel.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
---
 tools/testing/selftests/x86/syscall_arg_fault.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/x86/syscall_arg_fault.c b/tools/testing/selftests/x86/syscall_arg_fault.c
index 7db4fc9..d2548401 100644
--- a/tools/testing/selftests/x86/syscall_arg_fault.c
+++ b/tools/testing/selftests/x86/syscall_arg_fault.c
@@ -43,7 +43,7 @@ static sigjmp_buf jmpbuf;
 
 static volatile sig_atomic_t n_errs;
 
-static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
+static void sigsegv_or_sigbus(int sig, siginfo_t *info, void *ctx_void)
 {
 	ucontext_t *ctx = (ucontext_t*)ctx_void;
 
@@ -73,7 +73,13 @@ int main()
 	if (sigaltstack(&stack, NULL) != 0)
 		err(1, "sigaltstack");
 
-	sethandler(SIGSEGV, sigsegv, SA_ONSTACK);
+	sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
+	/*
+	 * The actual exception can vary.  On Atom CPUs, we get #SS
+	 * instead of #PF when the vDSO fails to access the stack when
+	 * ESP is too close to 2^32, and #SS causes SIGBUS.
+	 */
+	sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK);
 	sethandler(SIGILL, sigill, SA_ONSTACK);
 
 	/*
-- 
2.7.4

Re: [PATCH v3] selftests/x86: Support Atom for syscall_arg_fault test

[shuah]

On 4/19/19 1:10 AM, Tong Bo wrote:
> Atom-based CPUs trigger stack fault when invoke 32-bit SYSENTER instruction
> with invalid register values. So we also need SIGBUS handling in this case.
> 
> Following is assembly when the fault exception happens.
> 
> (gdb) disassemble $eip
> Dump of assembler code for function __kernel_vsyscall:
>     0xf7fd8fe0 <+0>:     push   %ecx
>     0xf7fd8fe1 <+1>:     push   %edx
>     0xf7fd8fe2 <+2>:     push   %ebp
>     0xf7fd8fe3 <+3>:     mov    %esp,%ebp
>     0xf7fd8fe5 <+5>:     sysenter
>     0xf7fd8fe7 <+7>:     int    $0x80
> => 0xf7fd8fe9 <+9>:     pop    %ebp
>     0xf7fd8fea <+10>:    pop    %edx
>     0xf7fd8feb <+11>:    pop    %ecx
>     0xf7fd8fec <+12>:    ret
> End of assembler dump.
> 
> According to Intel SDM, this could also be a Stack Segment Fault(#SS, 12),
> except a normal Page Fault(#PF, 14). Especially, in section 6.9 of Vol.3A,
> both stack and page faults are within the 10th(lowest priority) class, and
> as it said, "exceptions within each class are implementation-dependent and
> may vary from processor to processor". It's expected for processors like
> Intel Atom to trigger stack fault(SIGBUS), while we get page fault(SIGSEGV)
> from common Core processors.
> 
> Signed-off-by: Tong Bo <bo.tong@intel.com>
> Acked-by: Andy Lutomirski <luto@kernel.org>
> ---
>   tools/testing/selftests/x86/syscall_arg_fault.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/x86/syscall_arg_fault.c b/tools/testing/selftests/x86/syscall_arg_fault.c
> index 7db4fc9..d2548401 100644
> --- a/tools/testing/selftests/x86/syscall_arg_fault.c
> +++ b/tools/testing/selftests/x86/syscall_arg_fault.c
> @@ -43,7 +43,7 @@ static sigjmp_buf jmpbuf;
>   
>   static volatile sig_atomic_t n_errs;
>   
> -static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
> +static void sigsegv_or_sigbus(int sig, siginfo_t *info, void *ctx_void)
>   {
>   	ucontext_t *ctx = (ucontext_t*)ctx_void;
>   
> @@ -73,7 +73,13 @@ int main()
>   	if (sigaltstack(&stack, NULL) != 0)
>   		err(1, "sigaltstack");
>   
> -	sethandler(SIGSEGV, sigsegv, SA_ONSTACK);
> +	sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
> +	/*
> +	 * The actual exception can vary.  On Atom CPUs, we get #SS
> +	 * instead of #PF when the vDSO fails to access the stack when
> +	 * ESP is too close to 2^32, and #SS causes SIGBUS.
> +	 */
> +	sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK);
>   	sethandler(SIGILL, sigill, SA_ONSTACK);
>   
>   	/*
> 

In case there is a dependency on x86 tree, here is my Ack

Acked-by: Shuah Khan <skhan@linuxfoundation.org>

thanks,
-- Shuah

RE: [PATCH v3] selftests/x86: Support Atom for syscall_arg_fault test

[Tong, Bo]

Is this patch going to be merged? Or still any blocking issue there?

Thanks,
Bo

-----Original Message-----
From: shuah [mailto:shuah@kernel.org] 
Sent: Friday, April 19, 2019 10:05 PM
To: Tong, Bo <bo.tong@intel.com>; luto@kernel.org; x86@kernel.org
Cc: linux-kselftest@vger.kernel.org; linux-kernel@vger.kernel.org; skhan@linuxfoundation.org; shuah@kernel.org
Subject: Re: [PATCH v3] selftests/x86: Support Atom for syscall_arg_fault test

On 4/19/19 1:10 AM, Tong Bo wrote:
> Atom-based CPUs trigger stack fault when invoke 32-bit SYSENTER 
> instruction with invalid register values. So we also need SIGBUS handling in this case.
> 
> Following is assembly when the fault exception happens.
> 
> (gdb) disassemble $eip
> Dump of assembler code for function __kernel_vsyscall:
>     0xf7fd8fe0 <+0>:     push   %ecx
>     0xf7fd8fe1 <+1>:     push   %edx
>     0xf7fd8fe2 <+2>:     push   %ebp
>     0xf7fd8fe3 <+3>:     mov    %esp,%ebp
>     0xf7fd8fe5 <+5>:     sysenter
>     0xf7fd8fe7 <+7>:     int    $0x80
> => 0xf7fd8fe9 <+9>:     pop    %ebp
>     0xf7fd8fea <+10>:    pop    %edx
>     0xf7fd8feb <+11>:    pop    %ecx
>     0xf7fd8fec <+12>:    ret
> End of assembler dump.
> 
> According to Intel SDM, this could also be a Stack Segment Fault(#SS, 
> 12), except a normal Page Fault(#PF, 14). Especially, in section 6.9 
> of Vol.3A, both stack and page faults are within the 10th(lowest 
> priority) class, and as it said, "exceptions within each class are 
> implementation-dependent and may vary from processor to processor". 
> It's expected for processors like Intel Atom to trigger stack 
> fault(SIGBUS), while we get page fault(SIGSEGV) from common Core processors.
> 
> Signed-off-by: Tong Bo <bo.tong@intel.com>
> Acked-by: Andy Lutomirski <luto@kernel.org>
> ---
>   tools/testing/selftests/x86/syscall_arg_fault.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/x86/syscall_arg_fault.c 
> b/tools/testing/selftests/x86/syscall_arg_fault.c
> index 7db4fc9..d2548401 100644
> --- a/tools/testing/selftests/x86/syscall_arg_fault.c
> +++ b/tools/testing/selftests/x86/syscall_arg_fault.c
> @@ -43,7 +43,7 @@ static sigjmp_buf jmpbuf;
>   
>   static volatile sig_atomic_t n_errs;
>   
> -static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
> +static void sigsegv_or_sigbus(int sig, siginfo_t *info, void 
> +*ctx_void)
>   {
>   	ucontext_t *ctx = (ucontext_t*)ctx_void;
>   
> @@ -73,7 +73,13 @@ int main()
>   	if (sigaltstack(&stack, NULL) != 0)
>   		err(1, "sigaltstack");
>   
> -	sethandler(SIGSEGV, sigsegv, SA_ONSTACK);
> +	sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
> +	/*
> +	 * The actual exception can vary.  On Atom CPUs, we get #SS
> +	 * instead of #PF when the vDSO fails to access the stack when
> +	 * ESP is too close to 2^32, and #SS causes SIGBUS.
> +	 */
> +	sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK);
>   	sethandler(SIGILL, sigill, SA_ONSTACK);
>   
>   	/*
> 

In case there is a dependency on x86 tree, here is my Ack

Acked-by: Shuah Khan <skhan@linuxfoundation.org>

thanks,
-- Shuah

Re: [PATCH v3] selftests/x86: Support Atom for syscall_arg_fault test

[shuah]

Hi Bo,

On 5/17/19 1:02 AM, Tong, Bo wrote:
> Is this patch going to be merged? Or still any blocking issue there?
> 
> Thanks,
> Bo
> 
> -----Original Message-----
> From: shuah [mailto:shuah@kernel.org]
> Sent: Friday, April 19, 2019 10:05 PM
> To: Tong, Bo <bo.tong@intel.com>; luto@kernel.org; x86@kernel.org
> Cc: linux-kselftest@vger.kernel.org; linux-kernel@vger.kernel.org; skhan@linuxfoundation.org; shuah@kernel.org
> Subject: Re: [PATCH v3] selftests/x86: Support Atom for syscall_arg_fault test
> 
> On 4/19/19 1:10 AM, Tong Bo wrote:
>> Atom-based CPUs trigger stack fault when invoke 32-bit SYSENTER
>> instruction with invalid register values. So we also need SIGBUS handling in this case.
>>
>> Following is assembly when the fault exception happens.
>>
>> (gdb) disassemble $eip
>> Dump of assembler code for function __kernel_vsyscall:
>>      0xf7fd8fe0 <+0>:     push   %ecx
>>      0xf7fd8fe1 <+1>:     push   %edx
>>      0xf7fd8fe2 <+2>:     push   %ebp
>>      0xf7fd8fe3 <+3>:     mov    %esp,%ebp
>>      0xf7fd8fe5 <+5>:     sysenter
>>      0xf7fd8fe7 <+7>:     int    $0x80
>> => 0xf7fd8fe9 <+9>:     pop    %ebp
>>      0xf7fd8fea <+10>:    pop    %edx
>>      0xf7fd8feb <+11>:    pop    %ecx
>>      0xf7fd8fec <+12>:    ret
>> End of assembler dump.
>>
>> According to Intel SDM, this could also be a Stack Segment Fault(#SS,
>> 12), except a normal Page Fault(#PF, 14). Especially, in section 6.9
>> of Vol.3A, both stack and page faults are within the 10th(lowest
>> priority) class, and as it said, "exceptions within each class are
>> implementation-dependent and may vary from processor to processor".
>> It's expected for processors like Intel Atom to trigger stack
>> fault(SIGBUS), while we get page fault(SIGSEGV) from common Core processors.
>>
>> Signed-off-by: Tong Bo <bo.tong@intel.com>
>> Acked-by: Andy Lutomirski <luto@kernel.org>
>> ---
>>    tools/testing/selftests/x86/syscall_arg_fault.c | 10 ++++++++--
>>    1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/testing/selftests/x86/syscall_arg_fault.c
>> b/tools/testing/selftests/x86/syscall_arg_fault.c
>> index 7db4fc9..d2548401 100644
>> --- a/tools/testing/selftests/x86/syscall_arg_fault.c
>> +++ b/tools/testing/selftests/x86/syscall_arg_fault.c
>> @@ -43,7 +43,7 @@ static sigjmp_buf jmpbuf;
>>    
>>    static volatile sig_atomic_t n_errs;
>>    
>> -static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
>> +static void sigsegv_or_sigbus(int sig, siginfo_t *info, void
>> +*ctx_void)
>>    {
>>    	ucontext_t *ctx = (ucontext_t*)ctx_void;
>>    
>> @@ -73,7 +73,13 @@ int main()
>>    	if (sigaltstack(&stack, NULL) != 0)
>>    		err(1, "sigaltstack");
>>    
>> -	sethandler(SIGSEGV, sigsegv, SA_ONSTACK);
>> +	sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
>> +	/*
>> +	 * The actual exception can vary.  On Atom CPUs, we get #SS
>> +	 * instead of #PF when the vDSO fails to access the stack when
>> +	 * ESP is too close to 2^32, and #SS causes SIGBUS.
>> +	 */
>> +	sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK);
>>    	sethandler(SIGILL, sigill, SA_ONSTACK);
>>    
>>    	/*
>>
> 
> In case there is a dependency on x86 tree, here is my Ack
> 
> Acked-by: Shuah Khan <skhan@linuxfoundation.org>
> 

Looks like it got left behind in the confusion of which tree.

I will apply this to my tree.

thanks,
-- Shuah