From: Celeste Liu coelacanthushex@gmail.com
[ Upstream commit 52449c17bdd1540940e21511612b58acebc49c06 ]
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 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 Tested-by: Emil Renner Berthing emil.renner.berthing@canonical.com Reviewed-by: Björn Töpel bjorn@rivosinc.com Reviewed-by: Guo Ren guoren@kernel.org Link: https://lore.kernel.org/r/20230801141607.435192-1-CoelacanthusHex@gmail.com Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 8c258b78c925c..bd19e885dcec1 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -268,16 +268,16 @@ 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;
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);