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/scall64-o32.S b/arch/mips/kernel/scall64-o32.S
index 91b43ee..f4f28b1 100644
--- a/arch/mips/kernel/scall64-o32.S
+++ b/arch/mips/kernel/scall64-o32.S
@@ -52,9 +52,6 @@
sll a2, a2, 0
sll a3, a3, 0
- dsll t0, v0, 3 # offset into table
- ld t2, (sys32_call_table - (__NR_O32_Linux * 8))(t0)
-
sd a3, PT_R26(sp) # save a3 for syscall restarting
/*
@@ -88,6 +85,9 @@
bnez t0, trace_a_syscall
syscall_common:
+ dsll t0, v0, 3 # offset into table
+ ld t2, (sys32_call_table - (__NR_O32_Linux * 8))(t0)
+
jalr t2 # Do The Real Thing (TM)
li t0, -EMAXERRNO - 1 # error?
@@ -112,7 +112,6 @@
sd a6, PT_R10(sp)
sd a7, PT_R11(sp) # For indirect syscalls
- move s0, t2 # Save syscall pointer
move a0, sp
/*
* absolute syscall number is in v0 unless we called syscall(__NR_###)
@@ -133,8 +132,8 @@
bltz v0, 1f # seccomp failed? Skip syscall
- move t2, s0
RESTORE_STATIC
+ ld v0, PT_R2(sp) # Restore syscall (maybe modified)
ld a0, PT_R4(sp) # Restore argument registers
ld a1, PT_R5(sp)
ld a2, PT_R6(sp)
@@ -143,6 +142,11 @@
ld a5, PT_R9(sp)
ld a6, PT_R10(sp)
ld a7, PT_R11(sp) # For indirect syscalls
+
+ dsubu t0, v0, __NR_O32_Linux # check (new) syscall number
+ sltiu t0, t0, __NR_O32_Linux_syscalls + 1
+ beqz t0, not_o32_scall
+
j syscall_common
1: j syscall_exit
