MIPS: scall: Handle seccomp filters which redirect syscalls
Commit d218af78492a ("MIPS: scall: Always run the seccomp syscall
filters") modified the syscall code to always call the seccomp filters,
but missed the case where a filter may redirect the syscall, as
revealed by the seccomp_bpf self test.
The syscall path now restores the syscall from the stack after the
filter rather than saving it locally. Syscall number checking and
syscall function table lookup is done after the filter may have run such
that redirected syscalls are also checked, and executed.
The regular path of syscall number checking and pointer lookup is also
made more consistent between ABIs with scall64-64.S being the reference.
With this patch in place, the seccomp_bpf self test now passes
TRACE_syscall.syscall_redirected and TRACE_syscall.syscall_dropped on
all MIPS ABIs.
Fixes: d218af78492a ("MIPS: scall: Always run the seccomp syscall filters")
Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Eric B Munson <emunson@akamai.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mips@linux-mips.org
Cc: IMG-MIPSLinuxKerneldevelopers@imgtec.com
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12916/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/kernel/scall32-o32.S b/arch/mips/kernel/scall32-o32.S
index d01fe53..c8e43e0 100644
--- a/arch/mips/kernel/scall32-o32.S
+++ b/arch/mips/kernel/scall32-o32.S
@@ -35,7 +35,6 @@
lw t1, PT_EPC(sp) # skip syscall on return
- subu v0, v0, __NR_O32_Linux # check syscall number
addiu t1, 4 # skip to next instruction
sw t1, PT_EPC(sp)
@@ -89,6 +88,7 @@
and t0, t1
bnez t0, syscall_trace_entry # -> yes
syscall_common:
+ subu v0, v0, __NR_O32_Linux # check syscall number
sltiu t0, v0, __NR_O32_Linux_syscalls + 1
beqz t0, illegal_syscall
@@ -118,24 +118,23 @@
syscall_trace_entry:
SAVE_STATIC
- move s0, v0
move a0, sp
/*
* syscall number is in v0 unless we called syscall(__NR_###)
* where the real syscall number is in a0
*/
- addiu a1, v0, __NR_O32_Linux
- bnez v0, 1f /* __NR_syscall at offset 0 */
+ move a1, v0
+ subu t2, v0, __NR_O32_Linux
+ bnez t2, 1f /* __NR_syscall at offset 0 */
lw a1, PT_R4(sp)
1: jal syscall_trace_enter
bltz v0, 1f # seccomp failed? Skip syscall
- move v0, s0 # restore syscall
-
RESTORE_STATIC
+ lw v0, PT_R2(sp) # Restore syscall (maybe modified)
lw a0, PT_R4(sp) # Restore argument registers
lw a1, PT_R5(sp)
lw a2, PT_R6(sp)