With CONFIG_FORTIFY_SOURCE enabled, string functions will also perform
dynamic checks using __builtin_object_size(ptr), which when failed will
panic the kernel.
Because the KASAN test deliberately performs out-of-bounds operations,
the kernel panics with FORITY_SOURCE, for example:
| kernel BUG at lib/string_helpers.c:910!
| invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
| CPU: 1 PID: 137 Comm: kunit_try_catch Tainted: G B 5.16.0-rc3+ #3
| Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
| RIP: 0010:fortify_panic+0x19/0x1b
| ...
| Call Trace:
| <TASK>
| kmalloc_oob_in_memset.cold+0x16/0x16
| ...
Fix it by also hiding `ptr` from the optimizer, which will ensure that
__builtin_object_size() does not return a valid size, preventing
fortified string functions from panicking.
Reported-by: Nico Pache <[email protected]>
Signed-off-by: Marco Elver <[email protected]>
---
lib/test_kasan.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 847cdbefab46..26a5c9007653 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -492,6 +492,7 @@ static void kmalloc_oob_in_memset(struct kunit *test)
ptr = kmalloc(size, GFP_KERNEL);
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+ OPTIMIZER_HIDE_VAR(ptr);
OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test,
memset(ptr, 0, size + KASAN_GRANULE_SIZE));
@@ -515,6 +516,7 @@ static void kmalloc_memmove_negative_size(struct kunit *test)
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
memset((char *)ptr, 0, 64);
+ OPTIMIZER_HIDE_VAR(ptr);
OPTIMIZER_HIDE_VAR(invalid_size);
KUNIT_EXPECT_KASAN_FAIL(test,
memmove((char *)ptr, (char *)ptr + 4, invalid_size));
@@ -531,6 +533,7 @@ static void kmalloc_memmove_invalid_size(struct kunit *test)
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
memset((char *)ptr, 0, 64);
+ OPTIMIZER_HIDE_VAR(ptr);
KUNIT_EXPECT_KASAN_FAIL(test,
memmove((char *)ptr, (char *)ptr + 4, invalid_size));
kfree(ptr);
@@ -893,6 +896,7 @@ static void kasan_memchr(struct kunit *test)
ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+ OPTIMIZER_HIDE_VAR(ptr);
OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test,
kasan_ptr_result = memchr(ptr, '1', size + 1));
@@ -919,6 +923,7 @@ static void kasan_memcmp(struct kunit *test)
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
memset(arr, 0, sizeof(arr));
+ OPTIMIZER_HIDE_VAR(ptr);
OPTIMIZER_HIDE_VAR(size);
KUNIT_EXPECT_KASAN_FAIL(test,
kasan_int_result = memcmp(ptr, arr, size+1));
--
2.35.0.rc0.227.g00780c9af4-goog
-On Mon, Jan 24, 2022 at 5:07 PM Marco Elver <[email protected]> wrote:
>
> With CONFIG_FORTIFY_SOURCE enabled, string functions will also perform
> dynamic checks using __builtin_object_size(ptr), which when failed will
> panic the kernel.
>
> Because the KASAN test deliberately performs out-of-bounds operations,
> the kernel panics with FORITY_SOURCE, for example:
Nit: FORITY_SOURCE -> FORTIFY_SOURCE
>
> | kernel BUG at lib/string_helpers.c:910!
> | invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
> | CPU: 1 PID: 137 Comm: kunit_try_catch Tainted: G B 5.16.0-rc3+ #3
> | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
> | RIP: 0010:fortify_panic+0x19/0x1b
> | ...
> | Call Trace:
> | <TASK>
> | kmalloc_oob_in_memset.cold+0x16/0x16
> | ...
>
> Fix it by also hiding `ptr` from the optimizer, which will ensure that
> __builtin_object_size() does not return a valid size, preventing
> fortified string functions from panicking.
>
> Reported-by: Nico Pache <[email protected]>
> Signed-off-by: Marco Elver <[email protected]>
> ---
> lib/test_kasan.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 847cdbefab46..26a5c9007653 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -492,6 +492,7 @@ static void kmalloc_oob_in_memset(struct kunit *test)
> ptr = kmalloc(size, GFP_KERNEL);
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> + OPTIMIZER_HIDE_VAR(ptr);
> OPTIMIZER_HIDE_VAR(size);
> KUNIT_EXPECT_KASAN_FAIL(test,
> memset(ptr, 0, size + KASAN_GRANULE_SIZE));
> @@ -515,6 +516,7 @@ static void kmalloc_memmove_negative_size(struct kunit *test)
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> memset((char *)ptr, 0, 64);
> + OPTIMIZER_HIDE_VAR(ptr);
> OPTIMIZER_HIDE_VAR(invalid_size);
> KUNIT_EXPECT_KASAN_FAIL(test,
> memmove((char *)ptr, (char *)ptr + 4, invalid_size));
> @@ -531,6 +533,7 @@ static void kmalloc_memmove_invalid_size(struct kunit *test)
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> memset((char *)ptr, 0, 64);
> + OPTIMIZER_HIDE_VAR(ptr);
> KUNIT_EXPECT_KASAN_FAIL(test,
> memmove((char *)ptr, (char *)ptr + 4, invalid_size));
> kfree(ptr);
> @@ -893,6 +896,7 @@ static void kasan_memchr(struct kunit *test)
> ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> + OPTIMIZER_HIDE_VAR(ptr);
> OPTIMIZER_HIDE_VAR(size);
> KUNIT_EXPECT_KASAN_FAIL(test,
> kasan_ptr_result = memchr(ptr, '1', size + 1));
> @@ -919,6 +923,7 @@ static void kasan_memcmp(struct kunit *test)
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> memset(arr, 0, sizeof(arr));
>
> + OPTIMIZER_HIDE_VAR(ptr);
> OPTIMIZER_HIDE_VAR(size);
> KUNIT_EXPECT_KASAN_FAIL(test,
> kasan_int_result = memcmp(ptr, arr, size+1));
> --
> 2.35.0.rc0.227.g00780c9af4-goog
>
Reviewed-by: Andrey Konovalov <[email protected]>
On Mon, 24 Jan 2022 at 18:54, Andrey Konovalov <[email protected]> wrote:
>
> -On Mon, Jan 24, 2022 at 5:07 PM Marco Elver <[email protected]> wrote:
> >
> > With CONFIG_FORTIFY_SOURCE enabled, string functions will also perform
> > dynamic checks using __builtin_object_size(ptr), which when failed will
> > panic the kernel.
> >
> > Because the KASAN test deliberately performs out-of-bounds operations,
> > the kernel panics with FORITY_SOURCE, for example:
>
> Nit: FORITY_SOURCE -> FORTIFY_SOURCE
How did that happen?! My hands need some better synchronization...
I'll refrain sending a v2, assuming Andrew can fix up this spelling
mistake upon applying.
[...]
>
> Reviewed-by: Andrey Konovalov <[email protected]>
Thanks!
On Mon, Jan 24, 2022 at 05:07:44PM +0100, Marco Elver wrote:
> With CONFIG_FORTIFY_SOURCE enabled, string functions will also perform
> dynamic checks using __builtin_object_size(ptr), which when failed will
> panic the kernel.
>
> Because the KASAN test deliberately performs out-of-bounds operations,
> the kernel panics with FORITY_SOURCE, for example:
>
> | kernel BUG at lib/string_helpers.c:910!
> | invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
> | CPU: 1 PID: 137 Comm: kunit_try_catch Tainted: G B 5.16.0-rc3+ #3
> | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
> | RIP: 0010:fortify_panic+0x19/0x1b
> | ...
> | Call Trace:
> | <TASK>
> | kmalloc_oob_in_memset.cold+0x16/0x16
> | ...
>
> Fix it by also hiding `ptr` from the optimizer, which will ensure that
> __builtin_object_size() does not return a valid size, preventing
> fortified string functions from panicking.
>
> Reported-by: Nico Pache <[email protected]>
> Signed-off-by: Marco Elver <[email protected]>
Yup, more good fixes. Thanks!
Reviewed-by: Kees Cook <[email protected]>
--
Kees Cook
On 1/24/22 11:07, Marco Elver wrote:
> With CONFIG_FORTIFY_SOURCE enabled, string functions will also perform
> dynamic checks using __builtin_object_size(ptr), which when failed will
> panic the kernel.
>
> Because the KASAN test deliberately performs out-of-bounds operations,
> the kernel panics with FORITY_SOURCE, for example:
>
> | kernel BUG at lib/string_helpers.c:910!
> | invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
> | CPU: 1 PID: 137 Comm: kunit_try_catch Tainted: G B 5.16.0-rc3+ #3
> | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
> | RIP: 0010:fortify_panic+0x19/0x1b
> | ...
> | Call Trace:
> | <TASK>
> | kmalloc_oob_in_memset.cold+0x16/0x16
> | ...
>
> Fix it by also hiding `ptr` from the optimizer, which will ensure that
> __builtin_object_size() does not return a valid size, preventing
> fortified string functions from panicking.
>
> Reported-by: Nico Pache <[email protected]>
> Signed-off-by: Marco Elver <[email protected]>
Looks good! Thanks for posting this Marco :)
Reviewed-by: Nico Pache <[email protected]>
> ---
> lib/test_kasan.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 847cdbefab46..26a5c9007653 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -492,6 +492,7 @@ static void kmalloc_oob_in_memset(struct kunit *test)
> ptr = kmalloc(size, GFP_KERNEL);
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> + OPTIMIZER_HIDE_VAR(ptr);
> OPTIMIZER_HIDE_VAR(size);
> KUNIT_EXPECT_KASAN_FAIL(test,
> memset(ptr, 0, size + KASAN_GRANULE_SIZE));
> @@ -515,6 +516,7 @@ static void kmalloc_memmove_negative_size(struct kunit *test)
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> memset((char *)ptr, 0, 64);
> + OPTIMIZER_HIDE_VAR(ptr);
> OPTIMIZER_HIDE_VAR(invalid_size);
> KUNIT_EXPECT_KASAN_FAIL(test,
> memmove((char *)ptr, (char *)ptr + 4, invalid_size));
> @@ -531,6 +533,7 @@ static void kmalloc_memmove_invalid_size(struct kunit *test)
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> memset((char *)ptr, 0, 64);
> + OPTIMIZER_HIDE_VAR(ptr);
> KUNIT_EXPECT_KASAN_FAIL(test,
> memmove((char *)ptr, (char *)ptr + 4, invalid_size));
> kfree(ptr);
> @@ -893,6 +896,7 @@ static void kasan_memchr(struct kunit *test)
> ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> + OPTIMIZER_HIDE_VAR(ptr);
> OPTIMIZER_HIDE_VAR(size);
> KUNIT_EXPECT_KASAN_FAIL(test,
> kasan_ptr_result = memchr(ptr, '1', size + 1));
> @@ -919,6 +923,7 @@ static void kasan_memcmp(struct kunit *test)
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> memset(arr, 0, sizeof(arr));
>
> + OPTIMIZER_HIDE_VAR(ptr);
> OPTIMIZER_HIDE_VAR(size);
> KUNIT_EXPECT_KASAN_FAIL(test,
> kasan_int_result = memcmp(ptr, arr, size+1));
>