From 61119394631f219e23ce98bcc3eb993a64a8ea64 Mon Sep 17 00:00:00 2001 From: Celeste Liu Date: Thu, 27 Jun 2024 22:23:39 +0800 Subject: [PATCH] riscv: entry: always initialize regs->a0 to -ENOSYS MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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" Reviewed-by: Björn Töpel Cc: stable@vger.kernel.org Signed-off-by: Celeste Liu Link: https://lore.kernel.org/r/20240627142338.5114-2-CoelacanthusHex@gmail.com Signed-off-by: Palmer Dabbelt --- 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).