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 unsigned wrap-around addition test to use check_add_overflow(), retaining the result for later usage (which removes the redundant open-coded addition). This paves the way to enabling the unsigned wrap-around sanitizer[2] 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: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Liam Howlett <liam.howlett@xxxxxxxxxx> Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: linux-m68k@xxxxxxxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- arch/m68k/kernel/sys_m68k.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/m68k/kernel/sys_m68k.c b/arch/m68k/kernel/sys_m68k.c index 1af5e6082467..b2b9248f2566 100644 --- a/arch/m68k/kernel/sys_m68k.c +++ b/arch/m68k/kernel/sys_m68k.c @@ -391,10 +391,11 @@ sys_cacheflush (unsigned long addr, int scope, int cache, unsigned long len) mmap_read_lock(current->mm); } else { + unsigned long sum; struct vm_area_struct *vma; /* Check for overflow. */ - if (addr + len < addr) + if (check_add_overflow(addr, len, &sum)) goto out; /* @@ -403,7 +404,7 @@ sys_cacheflush (unsigned long addr, int scope, int cache, unsigned long len) */ mmap_read_lock(current->mm); vma = vma_lookup(current->mm, addr); - if (!vma || addr + len > vma->vm_end) + if (!vma || sum > vma->vm_end) goto out_unlock; } -- 2.34.1
