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MIPS: scall: Handle seccomp filters which redirect syscalls 

Commit d218af7849 ("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: d218af7849 ("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>
hifive-unleashed-5.1
Matt Redfearn 2016-03-29 09:35:31 +01:00 committed by Ralf Baechle
parent 5050e91fa6
commit a400bed6d1
4 changed files with 24 additions and 18 deletions
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11
arch/mips/kernel/scall32-o32.S
View File

@ -35,7 +35,6 @@ NESTED(handle_sys, PT_SIZE, sp)
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 @@ loads_done:
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 @@ o32_syscall_exit:
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)

3
arch/mips/kernel/scall64-64.S
View File

@ -82,15 +82,14 @@ n64_syscall_exit:
syscall_trace_entry:
SAVE_STATIC
move s0, v0
move a0, sp
move a1, v0
jal syscall_trace_enter
bltz v0, 1f # seccomp failed? Skip syscall
move v0, 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)

14
arch/mips/kernel/scall64-n32.S
View File

@ -42,9 +42,6 @@ NESTED(handle_sysn32, PT_SIZE, sp)
#endif
beqz t0, not_n32_scall
dsll t0, v0, 3 # offset into table
ld t2, (sysn32_call_table - (__NR_N32_Linux * 8))(t0)
sd a3, PT_R26(sp) # save a3 for syscall restarting
li t1, _TIF_WORK_SYSCALL_ENTRY
@ -53,6 +50,9 @@ NESTED(handle_sysn32, PT_SIZE, sp)
bnez t0, n32_syscall_trace_entry
syscall_common:
dsll t0, v0, 3 # offset into table
ld t2, (sysn32_call_table - (__NR_N32_Linux * 8))(t0)
jalr t2 # Do The Real Thing (TM)
li t0, -EMAXERRNO - 1 # error?
@ -71,21 +71,25 @@ syscall_common:
n32_syscall_trace_entry:
SAVE_STATIC
move s0, t2
move a0, sp
move a1, v0
jal syscall_trace_enter
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)
ld a3, PT_R7(sp)
ld a4, PT_R8(sp)
ld a5, PT_R9(sp)
dsubu t2, v0, __NR_N32_Linux # check (new) syscall number
sltiu t0, t2, __NR_N32_Linux_syscalls + 1
beqz t0, not_n32_scall
j syscall_common
1: j syscall_exit

14
arch/mips/kernel/scall64-o32.S
View File

@ -52,9 +52,6 @@ NESTED(handle_sys, PT_SIZE, sp)
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 @@ loads_done:
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 @@ trace_a_syscall:
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 @@ trace_a_syscall:
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 @@ trace_a_syscall:
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