csky: Fix a4/a5 restoration in syscall trace path

abb81e5c · Hanlin Song <[email protected]> · 2026-05-22 11:18:24 +08:00

The syscall trace path reloads syscall arguments from pt_regs before
calling the syscall handler. On C-SKY ABIv2, the 5th and 6th syscall
arguments are prepared as stack arguments before invoking syscallid.

The current code adjusts sp before loading LSAVE_A4 and LSAVE_A5. Since
those offsets are relative to the original pt_regs base, loading them
after changing sp fetches the wrong slots. As a result, traced syscalls
that use the 5th or 6th argument may receive corrupted arguments.

This is visible with mmap2(), which takes six arguments. A small
PTRACE_SYSCALL reproducer opens a file and maps one page with:

  mmap(NULL, 4096, PROT_READ | PROT_EXEC, MAP_PRIVATE, fd, 0)

Before the fix, the traced child fails the mmap and exits with 12.
After the fix, the mapping succeeds and the child exits with 0.

Fix the trace path by loading a4/a5 from pt_regs before changing sp.

Tested on: ck860f, linux-4.19.15, C-SKY abiv2

Fixes: e0bbb53843b5 ("csky: Fixup abiv2 syscall_trace break a4 & a5")
Suggested-by: Guo Ren <[email protected]>
Signed-off-by: Hanlin Song <[email protected]>
Signed-off-by: Guo Ren (Alibaba DAMO Academy) <[email protected]>

Commit

abb81e5ce7d995baa41556b8125fa59e28ba3be8

Parents

dc59e4fe

Changes

1 files changed · +3 −3