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powerpc/64s/syscall: Use pt_regs.trap to distinguish syscall ABI difference between sc and scv syscalls

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The sc and scv 0 system calls have different ABI conventions, and
ptracers need to know which system call type is being used if they want
to look at the syscall registers.

Document that pt_regs.trap can be used for this, and fix one in-tree user
to work with scv 0 syscalls.

Fixes: 7fa95f9ada ("powerpc/64s: system call support for scv/rfscv instructions")
Cc: stable@vger.kernel.org # v5.9+
Reported-by: "Dmitry V. Levin" <ldv@altlinux.org>
Suggested-by: "Dmitry V. Levin" <ldv@altlinux.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210520111931.2597127-1-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2021-05-20 21:19:30 +10:00 committed by Michael Ellerman
parent e2f5efd0f0
commit 5665bc35c1
2 changed files with 28 additions and 9 deletions
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10
Documentation/powerpc/syscall64-abi.rst
View File

@ -109,6 +109,16 @@ auxiliary vector.
scv 0 syscalls will always behave as PPC_FEATURE2_HTM_NOSC.
ptrace
------
When ptracing system calls (PTRACE_SYSCALL), the pt_regs.trap value contains
the system call type that can be used to distinguish between sc and scv 0
system calls, and the different register conventions can be accounted for.
If the value of (pt_regs.trap & 0xfff0) is 0xc00 then the system call was
performed with the sc instruction, if it is 0x3000 then the system call was
performed with the scv 0 instruction.
vsyscall
========

27
tools/testing/selftests/seccomp/seccomp_bpf.c
View File

@ -1753,16 +1753,25 @@ TEST_F(TRACE_poke, getpid_runs_normally)
# define SYSCALL_RET_SET(_regs, _val) \
do { \
typeof(_val) _result = (_val); \
/* \
* A syscall error is signaled by CR0 SO bit \
* and the code is stored as a positive value. \
*/ \
if (_result < 0) { \
SYSCALL_RET(_regs) = -_result; \
(_regs).ccr |= 0x10000000; \
} else { \
if ((_regs.trap & 0xfff0) == 0x3000) { \
/* \
* scv 0 system call uses -ve result \
* for error, so no need to adjust. \
*/ \
SYSCALL_RET(_regs) = _result; \
(_regs).ccr &= ~0x10000000; \
} else { \
/* \
* A syscall error is signaled by the \
* CR0 SO bit and the code is stored as \
* a positive value. \
*/ \
if (_result < 0) { \
SYSCALL_RET(_regs) = -_result; \
(_regs).ccr |= 0x10000000; \
} else { \
SYSCALL_RET(_regs) = _result; \
(_regs).ccr &= ~0x10000000; \
} \
} \
} while (0)
# define SYSCALL_RET_SET_ON_PTRACE_EXIT