linux-kernel - RE: [RFC PATCH v3 0/2] selftests/x86: sysret

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Date:   Tue, 24 Jan 2023 21:32:14 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>,
        "H. Peter Anvin" <hpa@...or.com>, x86 Mailing List <x86@...nel.org>
CC:     "Hansen, Dave" <dave.hansen@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Shuah Khan <shuah@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linux Kselftest Mailing List 
        <linux-kselftest@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH v3 0/2] selftests/x86: sysret_rip update for FRED
 system

> From: Ammar Faizi <ammarfaizi2@...weeb.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@...el.com
> Fixes: 660602140103 ("selftests/x86: Add a selftest for SYSRET to noncanonical
> addresses")
> Link: https://lore.kernel.org/lkml/25b96960-a07e-a952-5c23-
> 786b55054126@...or.com
> Reported-by: Xin Li <xin3.li@...el.com>
> Co-developed-by: H. Peter Anvin (Intel) <hpa@...or.com>
> Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
> Acked-by: H. Peter Anvin (Intel) <hpa@...or.com>
> Signed-off-by: Ammar Faizi <ammarfaizi2@...weeb.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@...or.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