From: Evgenii Stepanov <eugenis@xxxxxxxxxx>
commit 3758a6c74e08bdc15ccccd6872a6ad37d165239a upstream.
In ex_handler_load_unaligned_zeropad() we erroneously extract the data and
addr register indices from ex->type rather than ex->data. As ex->type will
contain EX_TYPE_LOAD_UNALIGNED_ZEROPAD (i.e. 4):
* We'll always treat X0 as the address register, since EX_DATA_REG_ADDR is
extracted from bits [9:5]. Thus, we may attempt to dereference an
arbitrary address as X0 may hold an arbitrary value.
* We'll always treat X4 as the data register, since EX_DATA_REG_DATA is
extracted from bits [4:0]. Thus we will corrupt X4 and cause arbitrary
behaviour within load_unaligned_zeropad() and its caller.
Fix this by extracting both values from ex->data as originally intended.
On an MTE-enabled QEMU image we are hitting the following crash:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Call trace:
fixup_exception+0xc4/0x108
__do_kernel_fault+0x3c/0x268
do_tag_check_fault+0x3c/0x104
do_mem_abort+0x44/0xf4
el1_abort+0x40/0x64
el1h_64_sync_handler+0x60/0xa0
el1h_64_sync+0x7c/0x80
link_path_walk+0x150/0x344
path_openat+0xa0/0x7dc
do_filp_open+0xb8/0x168
do_sys_openat2+0x88/0x17c
__arm64_sys_openat+0x74/0xa0
invoke_syscall+0x48/0x148
el0_svc_common+0xb8/0xf8
do_el0_svc+0x28/0x88
el0_svc+0x24/0x84
el0t_64_sync_handler+0x88/0xec
el0t_64_sync+0x1b4/0x1b8
Code: f8695a69 71007d1f 540000e0 927df12a (f940014a)
Fixes: 753b32368705 ("arm64: extable: add load_unaligned_zeropad() handler")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.16.x
Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Evgenii Stepanov <eugenis@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220125182217.2605202-1-eugenis@xxxxxxxxxx
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/mm/extable.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/arm64/mm/extable.c
+++ b/arch/arm64/mm/extable.c
@@ -43,8 +43,8 @@ static bool
ex_handler_load_unaligned_zeropad(const struct exception_table_entry *ex,
struct pt_regs *regs)
{
- int reg_data = FIELD_GET(EX_DATA_REG_DATA, ex->type);
- int reg_addr = FIELD_GET(EX_DATA_REG_ADDR, ex->type);
+ int reg_data = FIELD_GET(EX_DATA_REG_DATA, ex->data);
+ int reg_addr = FIELD_GET(EX_DATA_REG_ADDR, ex->data);
unsigned long data, addr, offset;
addr = pt_regs_read_reg(regs, reg_addr);
