[PATCH 5.12 082/127] powerpc/64s/syscall: Use pt_regs.trap to distinguish syscall ABI difference between sc and scv syscalls

Greg Kroah-Hartman
2021-05-24T16:04:43Z

From: Nicholas Piggin <npiggin@gmail.com>

commit 5665bc35c1ed917ac8fd06cb651317bb47a65b10 upstream.

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: 7fa95f9adaee ("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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
Documentation/powerpc/syscall64-abi.rst | 10 +++++++++
tools/testing/selftests/seccomp/seccomp_bpf.c | 27 +++++++++++++++++---------
2 files changed, 28 insertions(+), 9 deletions(-)

--- a/Documentation/powerpc/syscall64-abi.rst
+++ b/Documentation/powerpc/syscall64-abi.rst
@@ -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
========

--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -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