[v2] libdw: check memory access in get_(u|s)leb128
Commit Message
From: Aleksei Vetrov <vvvvvv@google.com>
__libdw_get_uleb128 and __libdw_get_sleb128 should check if addrp has
already reached the end before unrolling the first step. It is done by
moving __libdw_max_len to the beginning of the function, which can
notice, that addrp is beyond the end. Then we just check the result of
this function.
Signed-off-by: Aleksei Vetrov <vvvvvv@google.com>
---
libdw/memory-access.h | 10 ++++++++--
tests/leb128.c | 29 ++++++++++++++++++++++++++++-
2 files changed, 36 insertions(+), 3 deletions(-)
Comments
Hi Aleksei,
On Mon, 2023-02-13 at 20:10 +0000, Aleksei Vetrov via Elfutils-devel
wrote:
> __libdw_get_uleb128 and __libdw_get_sleb128 should check if addrp has
> already reached the end before unrolling the first step. It is done by
> moving __libdw_max_len to the beginning of the function, which can
> notice, that addrp is beyond the end. Then we just check the result of
> this function.
This looks good. And I couldn't measure any meaningful performance
difference. Pushed.
Even though this now catches all calls that have start >= end, I'll
also push my other patch to add extra guards in the callers of
get_(u|s)leb128, because that does provide us with better error
messages.
Thanks,
Mark
@@ -72,13 +72,16 @@ __libdw_max_len_sleb128 (const unsigned char *addr, const unsigned char *end)
static inline uint64_t
__libdw_get_uleb128 (const unsigned char **addrp, const unsigned char *end)
{
+ const size_t max = __libdw_max_len_uleb128 (*addrp, end);
+ if (unlikely (max == 0))
+ return UINT64_MAX;
+
uint64_t acc = 0;
/* Unroll the first step to help the compiler optimize
for the common single-byte case. */
get_uleb128_step (acc, *addrp, 0);
- const size_t max = __libdw_max_len_uleb128 (*addrp - 1, end);
for (size_t i = 1; i < max; ++i)
get_uleb128_step (acc, *addrp, i);
/* Other implementations set VALUE to UINT_MAX in this
@@ -124,6 +127,10 @@ __libdw_get_uleb128_unchecked (const unsigned char **addrp)
static inline int64_t
__libdw_get_sleb128 (const unsigned char **addrp, const unsigned char *end)
{
+ const size_t max = __libdw_max_len_sleb128 (*addrp, end);
+ if (unlikely (max == 0))
+ return INT64_MAX;
+
/* Do the work in an unsigned type, but use implementation-defined
behavior to cast to signed on return. This avoids some undefined
behavior when shifting. */
@@ -133,7 +140,6 @@ __libdw_get_sleb128 (const unsigned char **addrp, const unsigned char *end)
for the common single-byte case. */
get_sleb128_step (acc, *addrp, 0);
- const size_t max = __libdw_max_len_sleb128 (*addrp - 1, end);
for (size_t i = 1; i < max; ++i)
get_sleb128_step (acc, *addrp, i);
if (*addrp == end)
@@ -117,6 +117,19 @@ test_sleb (void)
return OK;
}
+static int
+test_sleb_safety (void)
+{
+ const int64_t expected_error = INT64_MAX;
+ int64_t value;
+ const unsigned char *test = NULL;
+ get_sleb128 (value, test, test);
+ if (value != expected_error)
+ return FAIL;
+
+ return OK;
+}
+
static int
test_one_uleb (const unsigned char *data, size_t len, uint64_t expect)
{
@@ -166,8 +179,22 @@ test_uleb (void)
return OK;
}
+static int
+test_uleb_safety (void)
+{
+ const uint64_t expected_error = UINT64_MAX;
+ uint64_t value;
+ const unsigned char *test = NULL;
+ get_uleb128 (value, test, test);
+ if (value != expected_error)
+ return FAIL;
+
+ return OK;
+}
+
int
main (void)
{
- return test_sleb () || test_uleb ();
+ return test_sleb () || test_sleb_safety () || test_uleb ()
+ || test_uleb_safety ();
}