From: Celeste Liu <coelacanthushex@xxxxxxxxx>
[ 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@xxxxxxxxxxxxx>
Co-developed-by: Ruizhe Pan <c141028@xxxxxxxxx>
Signed-off-by: Ruizhe Pan <c141028@xxxxxxxxx>
Co-developed-by: Shiqi Zhang <shiqi@xxxxxxxxxxxxxxxx>
Signed-off-by: Shiqi Zhang <shiqi@xxxxxxxxxxxxxxxx>
Signed-off-by: Celeste Liu <CoelacanthusHex@xxxxxxxxx>
Tested-by: Felix Yan <felixonmars@xxxxxxxxxxxxx>
Tested-by: Emil Renner Berthing <emil.renner.berthing@xxxxxxxxxxxxx>
Reviewed-by: Björn Töpel <bjorn@xxxxxxxxxxxx>
Reviewed-by: Guo Ren <guoren@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230801141607.435192-1-CoelacanthusHex@xxxxxxxxx
Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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);
--
2.40.1
