[RFC PATCH v5 0/2] sysret_rip update for the Intel FRED architecture

[Ammar Faizi]

From: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>

This is an RFC patchset v5. There are two 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@xxxxxxxxx

#### 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@xxxxxxxxx>
Signed-off-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Signed-off-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>
---

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 | 146 +++++++++++++++++++++--
 1 file changed, 137 insertions(+), 9 deletions(-)


base-commit: e12ad468c22065a2826b2fc4c11d2113a7975301
-- 
Ammar Faizi