From 52449c17bdd1540940e21511612b58acebc49c06 Mon Sep 17 00:00:00 2001 From: Celeste Liu Date: Tue, 1 Aug 2023 22:15:16 +0800 Subject: [PATCH] riscv: entry: set a0 = -ENOSYS only when syscall != -1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 commit 9c2598d43510 ("riscv: entry: Save a0 prior syscall_enter_from_user_mode()"). After analysing code, we think that regs->a0 = -ENOSYS should only be executed when syscall != -1. 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 executed. 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 Co-developed-by: Ruizhe Pan Signed-off-by: Ruizhe Pan Co-developed-by: Shiqi Zhang Signed-off-by: Shiqi Zhang Signed-off-by: Celeste Liu Tested-by: Felix Yan Tested-by: Emil Renner Berthing Reviewed-by: Björn Töpel Reviewed-by: Guo Ren Link: https://lore.kernel.org/r/20230801141607.435192-1-CoelacanthusHex@gmail.com Signed-off-by: Palmer Dabbelt --- arch/riscv/kernel/traps.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index f910dfccbf5d..729f79c97e2b 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -297,7 +297,7 @@ asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs) asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs) { if (user_mode(regs)) { - ulong syscall = regs->a7; + long syscall = regs->a7; regs->epc += 4; regs->orig_a0 = regs->a0; @@ -306,9 +306,9 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs) syscall = syscall_enter_from_user_mode(regs, syscall); - if (syscall < NR_syscalls) + if (syscall >= 0 && syscall < NR_syscalls) syscall_handler(regs, syscall); - else + else if (syscall != -1) regs->a0 = -ENOSYS; syscall_exit_to_user_mode(regs);