riscv: entry: set a0 = -ENOSYS only when syscall != -1

Browse source

When we test seccomp with 6.4 kernel, we found errno has wrong value.
If we deny NETLINK_AUDIT with EAFNOSUPPORT, after f0bddf5058, we will
get ENOSYS instead. We got same result with commit 9c2598d435 ("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: f0bddf5058 ("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>

...

This commit is contained in:

Celeste Liu 2023-08-01 22:15:16 +08:00 • committed by Palmer Dabbelt

parent 7e3811521d

commit 52449c17bd

No known key found for this signature in database

GPG key ID: 2E1319F35FBB1889

1 changed files with 3 additions and 3 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

6

arch/riscv/kernel/traps.c

View file