[PATCH 4.19 016/267] ARM: 8977/1: ptrace: Fix mask for thumb breakpoint hook

Greg Kroah-Hartman
2020-06-19T16:30:22Z

From: Fredrik Strupe <fredrik@strupe.net>

[ Upstream commit 3866f217aaa81bf7165c7f27362eee5d7919c496 ]

call_undef_hook() in traps.c applies the same instr_mask for both 16-bit
and 32-bit thumb instructions. If instr_mask then is only 16 bits wide
(0xffff as opposed to 0xffffffff), the first half-word of 32-bit thumb
instructions will be masked out. This makes the function match 32-bit
thumb instructions where the second half-word is equal to instr_val,
regardless of the first half-word.

The result in this case is that all undefined 32-bit thumb instructions
with the second half-word equal to 0xde01 (udf #1) work as breakpoints
and will raise a SIGTRAP instead of a SIGILL, instead of just the one
intended 16-bit instruction. An example of such an instruction is
0xeaa0de01, which is unallocated according to Arm ARM and should raise a
SIGILL, but instead raises a SIGTRAP.

This patch fixes the issue by setting all the bits in instr_mask, which
will still match the intended 16-bit thumb instruction (where the
upper half is always 0), but not any 32-bit thumb instructions.

Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Fredrik Strupe <fredrik@strupe.net>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm/kernel/ptrace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 36718a424358..492ac74a63f4 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -229,8 +229,8 @@ static struct undef_hook arm_break_hook = {
};

static struct undef_hook thumb_break_hook = {
- .instr_mask = 0xffff,
- .instr_val = 0xde01,
+ .instr_mask = 0xffffffff,
+ .instr_val = 0x0000de01,
.cpsr_mask = PSR_T_BIT,
.cpsr_val = PSR_T_BIT,
.fn = break_trap,
--
2.25.1