linux-kernel - [PATCH 48/82] drm/nouveau/mmu: Refactor intentional wrap-around test

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Message-Id: <20240123002814.1396804-48-keescook@chromium.org>
Date: Mon, 22 Jan 2024 16:27:23 -0800
From: Kees Cook <keescook@...omium.org>
To: linux-hardening@...r.kernel.org
Cc: Kees Cook <keescook@...omium.org>,
	Karol Herbst <kherbst@...hat.com>,
	Lyude Paul <lyude@...hat.com>,
	Danilo Krummrich <dakr@...hat.com>,
	David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Dave Airlie <airlied@...hat.com>,
	Ben Skeggs <bskeggs@...hat.com>,
	dri-devel@...ts.freedesktop.org,
	nouveau@...ts.freedesktop.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 48/82] drm/nouveau/mmu: Refactor intentional wrap-around test

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: Karol Herbst <kherbst@...hat.com>
Cc: Lyude Paul <lyude@...hat.com>
Cc: Danilo Krummrich <dakr@...hat.com>
Cc: David Airlie <airlied@...il.com>
Cc: Daniel Vetter <daniel@...ll.ch>
Cc: Dave Airlie <airlied@...hat.com>
Cc: Ben Skeggs <bskeggs@...hat.com>
Cc: dri-devel@...ts.freedesktop.org
Cc: nouveau@...ts.freedesktop.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c b/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
index 6ca1a82ccbc1..87c0903be9a7 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
@@ -1291,7 +1291,7 @@ nvkm_vmm_pfn_map(struct nvkm_vmm *vmm, u8 shift, u64 addr, u64 size, u64 *pfn)
 
 	if (!page->shift || !IS_ALIGNED(addr, 1ULL << shift) ||
 			    !IS_ALIGNED(size, 1ULL << shift) ||
-	    addr + size < addr || addr + size > vmm->limit) {
+	    add_would_overflow(addr, size) || addr + size > vmm->limit) {
 		VMM_DEBUG(vmm, "paged map %d %d %016llx %016llx\n",
 			  shift, page->shift, addr, size);
 		return -EINVAL;
-- 
2.34.1