RE: [RFC PATCH v3 0/2] selftests/x86: sysret_rip update for FRED system

["H. Peter Anvin" <hpa@zytor.com>]

On January 24, 2023 1:32:14 PM PST, "Li, Xin3" <xin3.li@intel.com> wrote:
>> From: Ammar Faizi <ammarfaizi2@gnuweeb.org>
>> 
>> This is an RFC patchset v3:
>> sysret_rip test update for Intel FRED architecture.
>> 
>> Xin Li reported sysret_rip test fails at:
>> 
>>         assert(ctx->uc_mcontext.gregs[REG_EFL] ==
>>                ctx->uc_mcontext.gregs[REG_R11]);
>
>On FRED systems, flags is 0x200a93 and r11 is 0xfeedfacedeadbeef here.
>
>We need to remove or change this assertion, maybe:
>  assert(ctx->uc_mcontext.gregs[REG_EFL] == ctx->uc_mcontext.gregs[REG_R11] ||
>         r11_sentinel == ctx->uc_mcontext.gregs[REG_R11]);
>
>> 
>> in a FRED system. Let's handle the FRED system scenario too. The 'syscall'
>> instruction in a FRED system doesn't set %r11=%rflags.
>> 
>> There are two patches in this series.
>> 
>> How to test this:
>> 
>>   $ make -C tools/testing/selftests/x86
>>   $ tools/testing/selftests/x86/sysret_rip_64
>> 
>> Link: https://lore.kernel.org/lkml/5d4ad3e3-034f-c7da-d141-
>> 9c001c2343af@intel.com
>> Fixes: 660602140103 ("selftests/x86: Add a selftest for SYSRET to noncanonical
>> addresses")
>> Link: https://lore.kernel.org/lkml/25b96960-a07e-a952-5c23-
>> 786b55054126@zytor.com
>> Reported-by: Xin Li <xin3.li@intel.com>
>> Co-developed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
>> Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
>> Acked-by: H. Peter Anvin (Intel) <hpa@zytor.com>
>> Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
>> ---
>> 
>> ## Changelog v3:
>> 
>>    - Test that we don't get a mix of REGS_SAVED and REGS_SYSRET,
>>      which is a major part of the point (hpa).
>> 
>> ## Changelog v2:
>> 
>>    - Use "+r"(rsp) as the right way to avoid redzone problems
>>      per Andrew's comment (hpa).
>>      (Ref: https://lore.kernel.org/lkml/8f5c24df-514d-5d89-f58f-
>> ec8c3eb1e049@zytor.com )
>> 
>> ---
>> 
>> Ammar Faizi (2):
>>   selftests/x86: sysret_rip: Handle syscall in a FRED system
>>   selftests/x86: sysret_rip: Add more syscall tests with respect to `%rcx` and `%r11`
>> 
>>  tools/testing/selftests/x86/sysret_rip.c | 120 ++++++++++++++++++++++-
>>  1 file changed, 119 insertions(+), 1 deletion(-)
>> 
>> 
>> base-commit: e12ad468c22065a2826b2fc4c11d2113a7975301
>> --
>> Ammar Faizi
>
>

This should use check_regs_result() – which is exactly the reason I made that a separate function.