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: Marc Zyngier <m...@kernel.org>
Cc: Oliver Upton <oliver.up...@linux.dev>
Cc: James Morse <james.mo...@arm.com>
Cc: Suzuki K Poulose <suzuki.poul...@arm.com>
Cc: Zenghui Yu <yuzeng...@huawei.com>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Will Deacon <w...@kernel.org>
Cc: Reiji Watanabe <rei...@google.com>
Cc: Eric Auger <eric.au...@redhat.com>
Cc: Ricardo Koller <ricar...@google.com>
Cc: Raghavendra Rao Ananta <rana...@google.com>
Cc: Quentin Perret <qper...@google.com>
Cc: Jean-Philippe Brucker <jean-phili...@linaro.org>
Cc: linux-arm-ker...@lists.infradead.org
Cc: kvm...@lists.linux.dev
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
arch/arm64/kvm/vgic/vgic-kvm-device.c | 6 ++++--
arch/arm64/kvm/vgic/vgic-v2.c | 10 ++++++----
2 files changed, 10 insertions(+), 6 deletions(-)
diff --git a/arch/arm64/kvm/vgic/vgic-kvm-device.c
b/arch/arm64/kvm/vgic/vgic-kvm-device.c
index f48b8dab8b3d..0eec5344d203 100644
--- a/arch/arm64/kvm/vgic/vgic-kvm-device.c
+++ b/arch/arm64/kvm/vgic/vgic-kvm-device.c
@@ -18,17 +18,19 @@ int vgic_check_iorange(struct kvm *kvm, phys_addr_t ioaddr,
phys_addr_t addr, phys_addr_t alignment,
phys_addr_t size)
{
+ phys_addr_t sum;
+
if (!IS_VGIC_ADDR_UNDEF(ioaddr))
return -EEXIST;
if (!IS_ALIGNED(addr, alignment) || !IS_ALIGNED(size, alignment))
return -EINVAL;
- if (addr + size < addr)
+ if (check_add_overflow(addr, size, &sum))
return -EINVAL;
if (addr & ~kvm_phys_mask(&kvm->arch.mmu) ||
- (addr + size) > kvm_phys_size(&kvm->arch.mmu))
+ sum > kvm_phys_size(&kvm->arch.mmu))
return -E2BIG;
return 0;
diff --git a/arch/arm64/kvm/vgic/vgic-v2.c b/arch/arm64/kvm/vgic/vgic-v2.c
index 7e9cdb78f7ce..c8d1e965d3b7 100644
--- a/arch/arm64/kvm/vgic/vgic-v2.c
+++ b/arch/arm64/kvm/vgic/vgic-v2.c
@@ -273,14 +273,16 @@ void vgic_v2_enable(struct kvm_vcpu *vcpu)
/* check for overlapping regions and for regions crossing the end of memory */
static bool vgic_v2_check_base(gpa_t dist_base, gpa_t cpu_base)
{
- if (dist_base + KVM_VGIC_V2_DIST_SIZE < dist_base)
+ gpa_t dist_sum, cpu_sum;
+
+ if (check_add_overflow(dist_base, KVM_VGIC_V2_DIST_SIZE, &dist_sum))
return false;
- if (cpu_base + KVM_VGIC_V2_CPU_SIZE < cpu_base)
+ if (check_add_overflow(cpu_base, KVM_VGIC_V2_CPU_SIZE, &cpu_sum))
return false;
- if (dist_base + KVM_VGIC_V2_DIST_SIZE <= cpu_base)
+ if (dist_sum <= cpu_base)
return true;
- if (cpu_base + KVM_VGIC_V2_CPU_SIZE <= dist_base)
+ if (cpu_sum <= dist_base)
return true;
return false;
--
2.34.1
