linux-kernel - [RFC PATCH v6 0/3] sysret_rip update for the Intel FRED architecture

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Date:   Thu, 26 Jan 2023 04:17:11 +0700
From:   Ammar Faizi <ammarfaizi2@...weeb.org>
To:     "H. Peter Anvin" <hpa@...or.com>, Xin Li <xin3.li@...el.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Brian Gerst <brgerst@...il.com>,
        Borislav Petkov <bp@...en8.de>, Shuah Khan <shuah@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        x86 Mailing List <x86@...nel.org>,
        Linux Kselftest Mailing List 
        <linux-kselftest@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH v6 0/3] sysret_rip update for the Intel FRED architecture

From: Ammar Faizi <ammarfaizi2@...weeb.org>

Hi,

This is an RFC patchset v6. There are three patches in this series.

Xin Li reported that the sysret_rip test fails at:

        assert(ctx->uc_mcontext.gregs[REG_EFL] ==
               ctx->uc_mcontext.gregs[REG_R11]);

on the Intel FRED architecture. Let's handle the FRED system scenario
too. The 'syscall' instruction in a FRED system doesn't set %rcx=%rip
and %r11=%rflags.

Syscall and sysenter in a FRED system are treated equivalently to
software interrupts, e.g. INT 0x80. They do not modify any registers.

Link: https://lore.kernel.org/lkml/5d4ad3e3-034f-c7da-d141-9c001c2343af@intel.com

## Changelog v6:

   - Move the check-regs assertion in sigusr1() to check_regs_result()
     (HPA).

   - Add a new test just like sigusr1(), but don't modify REG_RCX and
     REG_R11. This is used to test SYSRET behavior consistency (HPA).

## Changelog v5:

   - Fix do_syscall() return value (Ammar).

## Changelog v4:

   - Fix the assertion condition inside the SIGUSR1 handler (Xin Li).

   - Explain the purpose of patch #2 in the commit message (HPA).

   - Update commit message (Ammar).

   - Repeat test_syscall_rcx_r11_consistent() 32 times to be more sure
     that the result is really consistent (Ammar).

## 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).


Co-developed-by: H. Peter Anvin (Intel) <hpa@...or.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
Signed-off-by: Ammar Faizi <ammarfaizi2@...weeb.org>
---

Ammar Faizi (3):
  selftests/x86: sysret_rip: Handle syscall in a FRED system
  selftests/x86: sysret_rip: Add more syscall tests with respect to `%rcx` and `%r11`
  selftests/x86: sysret_rip: Test opportunistic SYSRET

 tools/testing/selftests/x86/sysret_rip.c | 177 +++++++++++++++++++++--
 1 file changed, 168 insertions(+), 9 deletions(-)


base-commit: e12ad468c22065a2826b2fc4c11d2113a7975301
-- 
Ammar Faizi