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[RFC,v6,0/3] sysret_rip update for the Intel FRED architecture

Message ID 20230125211714.838216-1-ammarfaizi2@gnuweeb.org
Headers show
Series sysret_rip update for the Intel FRED architecture | expand

Message

Ammar Faizi Jan. 25, 2023, 9:17 p.m. UTC 
From: Ammar Faizi <ammarfaizi2@gnuweeb.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@zytor.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.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

Comments

Ammar Faizi Jan. 25, 2023, 11:01 p.m. UTC | #1 
On Thu, Jan 26, 2023 at 04:17:12AM +0700, Ammar Faizi wrote:
> +/*
> + * REGS_SAVED  = %rcx and %r11 preserved.
> + * REGS_SYSRET = %rcx and %r11 set to %rflags and %rip.
> + * REGS_ERROR  = %rcx and/or %r11 set to any other values.

Since we moved the assertion into check_regs_result(), we no longer
need REGS_ERROR. check_regs_result() is now a void function.

Will remove that comment...