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 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: Sean Christopherson <seanjc@xxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: x86@xxxxxxxxxx Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: kvm@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- arch/x86/kvm/svm/sev.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index f760106c31f8..12a6a2b1ac81 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -400,16 +400,17 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr, unsigned long locked, lock_limit; struct page **pages; unsigned long first, last; + unsigned long sum; int ret; lockdep_assert_held(&kvm->lock); - if (ulen == 0 || uaddr + ulen < uaddr) + if (ulen == 0 || check_add_overflow(uaddr, ulen, &sum)) return ERR_PTR(-EINVAL); /* Calculate number of pages. */ first = (uaddr & PAGE_MASK) >> PAGE_SHIFT; - last = ((uaddr + ulen - 1) & PAGE_MASK) >> PAGE_SHIFT; + last = ((sum - 1) & PAGE_MASK) >> PAGE_SHIFT; npages = (last - first + 1); locked = sev->pages_locked + npages; -- 2.34.1
