path: root/arch/arm64/include/asm/futex.h
diff options
authorWill Deacon <will.deacon@arm.com>2017-04-05 11:14:05 +0100
committerWill Deacon <will.deacon@arm.com>2017-05-30 11:07:42 +0100
commit5f16a046f8e144c294ef98cd29d9458b5f8273e5 (patch)
treec72f04ee1d06040c708ed5814e94712f9193b2be /arch/arm64/include/asm/futex.h
parentarm64: check return value of of_flat_dt_get_machine_name (diff)
arm64: futex: Fix undefined behaviour with FUTEX_OP_OPARG_SHIFT usage
FUTEX_OP_OPARG_SHIFT instructs the futex code to treat the 12-bit oparg field as a shift value, potentially leading to a left shift value that is negative or with an absolute value that is significantly larger then the size of the type. UBSAN chokes with: ================================================================================ UBSAN: Undefined behaviour in ./arch/arm64/include/asm/futex.h:60:13 shift exponent -1 is negative CPU: 1 PID: 1449 Comm: syz-executor0 Not tainted 4.11.0-rc4-00005-g977eb52-dirty #11 Hardware name: linux,dummy-virt (DT) Call trace: [<ffff200008094778>] dump_backtrace+0x0/0x538 arch/arm64/kernel/traps.c:73 [<ffff200008094cd0>] show_stack+0x20/0x30 arch/arm64/kernel/traps.c:228 [<ffff200008c194a8>] __dump_stack lib/dump_stack.c:16 [inline] [<ffff200008c194a8>] dump_stack+0x120/0x188 lib/dump_stack.c:52 [<ffff200008cc24b8>] ubsan_epilogue+0x18/0x98 lib/ubsan.c:164 [<ffff200008cc3098>] __ubsan_handle_shift_out_of_bounds+0x250/0x294 lib/ubsan.c:421 [<ffff20000832002c>] futex_atomic_op_inuser arch/arm64/include/asm/futex.h:60 [inline] [<ffff20000832002c>] futex_wake_op kernel/futex.c:1489 [inline] [<ffff20000832002c>] do_futex+0x137c/0x1740 kernel/futex.c:3231 [<ffff200008320504>] SYSC_futex kernel/futex.c:3281 [inline] [<ffff200008320504>] SyS_futex+0x114/0x268 kernel/futex.c:3249 [<ffff200008084770>] el0_svc_naked+0x24/0x28 ================================================================================ syz-executor1 uses obsolete (PF_INET,SOCK_PACKET) sock: process `syz-executor0' is using obsolete setsockopt SO_BSDCOMPAT This patch attempts to fix some of this by: * Making encoded_op an unsigned type, so we can shift it left even if the top bit is set. * Casting to signed prior to shifting right when extracting oparg and cmparg * Consider only the bottom 5 bits of oparg when using it as a left-shift value. Whilst I think this catches all of the issues, I'd much prefer to remove this stuff, as I think it's unused and the bugs are copy-pasted between a bunch of architectures. Reviewed-by: Robin Murphy <robin.murphy@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to '')
1 files changed, 4 insertions, 4 deletions
diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index 85c4a8981d47..f32b42e8725d 100644
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -48,16 +48,16 @@ do { \
} while (0)
static inline int
-futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
+futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
int op = (encoded_op >> 28) & 7;
int cmp = (encoded_op >> 24) & 15;
- int oparg = (encoded_op << 8) >> 20;
- int cmparg = (encoded_op << 20) >> 20;
+ int oparg = (int)(encoded_op << 8) >> 20;
+ int cmparg = (int)(encoded_op << 20) >> 20;
int oldval = 0, ret, tmp;
if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
- oparg = 1 << oparg;
+ oparg = 1U << (oparg & 0x1f);
if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
return -EFAULT;