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@xxxxxxxxxx]
> Sent: Friday, April 19, 2019 10:05 PM
> To: Tong, Bo <bo.tong@xxxxxxxxx>; luto@xxxxxxxxxx; x86@xxxxxxxxxx
> Cc: linux-kselftest@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; skhan@xxxxxxxxxxxxxxxxxxx; shuah@xxxxxxxxxx
> 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@xxxxxxxxx>
> > Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>
> > ---
> >    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@xxxxxxxxxxxxxxxxxxx>

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

I will apply this to my tree.

thanks,
-- Shuah