From: Celeste Liu coelacanthushex@gmail.com
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 Link: https://lore.kernel.org/r/20240627142338.5114-2-CoelacanthusHex@gmail.com Signed-off-by: Palmer Dabbelt palmer@rivosinc.com (cherry picked from commit 61119394631f219e23ce98bcc3eb993a64a8ea64) --- arch/riscv/kernel/traps.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index 67d0073fb624..2158b7a65d74 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -311,6 +311,7 @@ asmlinkage __visible __trap_section 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);
@@ -318,8 +319,6 @@ asmlinkage __visible __trap_section 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;
syscall_exit_to_user_mode(regs); } else {