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

Li, Xin3
2023-01-24T21:32:29Z

> 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