[PATCH 2/2] tools/x86: Fix some potential undefined behavior

Ian Rogers
2020-10-15T06:22:02Z

From: Numfor Mbiziwo-Tiapo <nums@google.com>

If insn_init is given a NULL kaddr and 0 buflen then validate_next will
perform arithmetic on NULL, add a guard to avoid this.

Don't perform unaligned loads in __get_next and __peek_nbyte_next as
these are forms of undefined behavior.

These problems were identified using the undefined behavior sanitizer
(ubsan) with perf test. Part of this patch was previously posted here:
https://lore.kernel.org/lkml/20190724184512.162887-4-nums@google.com/

Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com>
---
tools/arch/x86/lib/insn.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/arch/x86/lib/insn.c b/tools/arch/x86/lib/insn.c
index 0151dfc6da61..e8874a8cac2c 100644
--- a/tools/arch/x86/lib/insn.c
+++ b/tools/arch/x86/lib/insn.c
@@ -17,13 +17,13 @@

/* Verify next sizeof(t) bytes can be on the same instruction */
#define validate_next(t, insn, n) \
- ((insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)
+ ((insn)->end_kaddr != 0 && (insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)

#define __get_next(t, insn) \
- ({ t r = *(t*)insn->next_byte; insn->next_byte += sizeof(t); r; })
+ ({ t r; memcpy(&r, insn->next_byte, sizeof(t)); insn->next_byte += sizeof(t); r; })

#define __peek_nbyte_next(t, insn, n) \
- ({ t r = *(t*)((insn)->next_byte + n); r; })
+ ({ t r; memcpy(&r, (insn)->next_byte + n, sizeof(t)); r; })

#define get_next(t, insn) \
({ if (unlikely(!validate_next(t, insn, 0))) goto err_out; __get_next(t, insn); })
--
2.28.0.1011.ga647a8990f-goog