diff mbox series

[65/82] nios2: Refactor intentional wrap-around test

Message ID 20240123002814.1396804-65-keescook@chromium.org
State New
Headers
Series overflow: Refactor open-coded arithmetic wrap-around |

Commit Message

Kees Cook Jan. 23, 2024, 12:27 a.m. UTC 
  In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:

	VAR + value < VAR

Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.

Refactor open-coded wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers in the future.

Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Ley Foon Tan <ley.foon.tan@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/nios2/kernel/sys_nios2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Dinh Nguyen Jan. 23, 2024, 1:15 p.m. UTC | #1 
On 1/22/24 18:27, Kees Cook wrote:
> In an effort to separate intentional arithmetic wrap-around from
> unexpected wrap-around, we need to refactor places that depend on this
> kind of math. One of the most common code patterns of this is:
> 
> 	VAR + value < VAR
> 
> Notably, this is considered "undefined behavior" for signed and pointer
> types, which the kernel works around by using the -fno-strict-overflow
> option in the build[1] (which used to just be -fwrapv). Regardless, we
> want to get the kernel source to the position where we can meaningfully
> instrument arithmetic wrap-around conditions and catch them when they
> are unexpected, regardless of whether they are signed[2], unsigned[3],
> or pointer[4] types.
> 
> Refactor open-coded wrap-around addition test to use add_would_overflow().
> This paves the way to enabling the wrap-around sanitizers in the future.
> 
> Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
> Link: https://github.com/KSPP/linux/issues/26 [2]
> Link: https://github.com/KSPP/linux/issues/27 [3]
> Link: https://github.com/KSPP/linux/issues/344 [4]
> Cc: Dinh Nguyen <dinguyen@kernel.org>
> Cc: Jann Horn <jannh@google.com>
> Cc: Ley Foon Tan <ley.foon.tan@intel.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>   arch/nios2/kernel/sys_nios2.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 

Acked-by: Dinh Nguyen <dinguyen@kernel.org>
diff mbox series

Patch

diff --git a/arch/nios2/kernel/sys_nios2.c b/arch/nios2/kernel/sys_nios2.c
index b1ca85699952..df53efdc96e3 100644
--- a/arch/nios2/kernel/sys_nios2.c
+++ b/arch/nios2/kernel/sys_nios2.c
@@ -32,7 +32,7 @@  asmlinkage int sys_cacheflush(unsigned long addr, unsigned long len,
 		return -EINVAL;
 
 	/* Check for overflow */
-	if (addr + len < addr)
+	if (add_would_overflow(addr, len))
 		return -EFAULT;
 
 	if (mmap_read_lock_killable(mm))