| Message ID | 20230718162940.226118-1-CoelacanthusHex@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] riscv: entry: set a0 prior to syscall_enter_from_user_mode | expand |
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index f910dfccbf5d2..ccadb5ffd063c 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -301,6 +301,7 @@ 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); @@ -308,8 +309,6 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs) if (syscall < NR_syscalls) syscall_handler(regs, syscall); - else - regs->a0 = -ENOSYS; syscall_exit_to_user_mode(regs); } else {
When we test seccomp with 6.4 kernel, we found errno has wrong value. If we deny NETLINK_AUDIT with EAFNOSUPPORT, after f0bddf50586d, we will get ENOSYS instead. We got same result with 9c2598d43510 ("riscv: entry: Save a0 prior syscall_enter_from_user_mode()"). After analysing code, we think that regs->a0 = -ENOSYS should be advanced before syscall_enter_from_user_mode to fix this problem. In __seccomp_filter, when seccomp rejected this syscall with specified errno, they will set a0 to return number as syscall ABI, and then return -1. This return number is finally pass as return number of syscall_enter_from_user_mode, and then is compared with NR_syscalls after converted to ulong (so it will be ULONG_MAX). The condition syscall < NR_syscalls will always be false, so regs->a0 = -ENOSYS is always executable. It covered a0 set by seccomp, so we always get ENOSYS when match seccomp RET_ERRNO rule. Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry") Reported-by: Felix Yan <felixonmars@archlinux.org> Co-developed-by: Ruizhe Pan <c141028@gmail.com> Signed-off-by: Ruizhe Pan <c141028@gmail.com> Co-developed-by: Shiqi Zhang <shiqi@isrc.iscas.ac.cn> Signed-off-by: Shiqi Zhang <shiqi@isrc.iscas.ac.cn> Signed-off-by: Celeste Liu <CoelacanthusHex@gmail.com> Tested-by: Felix Yan <felixonmars@archlinux.org> --- v1 -> v2: added explanation on why always got ENOSYS arch/riscv/kernel/traps.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)