Otherwise when the tracer changes syscall number to -1, the kernel fails to initialize a0 with -ENOSYS and subsequently fails to return the error code of the failed syscall to userspace. For example, it will break strace syscall tampering.

Fixes: 52449c17bdd1 ("riscv: entry: set a0 = -ENOSYS only when syscall != -1") Reported-by: "Dmitry V. Levin" ldv@strace.io Reviewed-by: Björn Töpel bjorn@rivosinc.com Cc: stable@vger.kernel.org Signed-off-by: Celeste Liu CoelacanthusHex@gmail.com --- arch/riscv/kernel/traps.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index 05a16b1f0aee..51ebfd23e007 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -319,6 +319,7 @@ void do_trap_ecall_u(struct pt_regs *regs)

regs->epc += 4; regs->orig_a0 = regs->a0; + regs->a0 = -ENOSYS;

riscv_v_vstate_discard(regs);

@@ -328,8 +329,7 @@ void do_trap_ecall_u(struct pt_regs *regs)

if (syscall >= 0 && syscall < NR_syscalls) syscall_handler(regs, syscall); - else if (syscall != -1) - regs->a0 = -ENOSYS; + /* * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), * so the maximum stack offset is 1k bytes (10 bits).