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

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