| Message ID | 20240123002814.1396804-22-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | overflow: Refactor open-coded arithmetic wrap-around | expand |
On Tue Jan 23, 2024 at 12:26 AM UTC, 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 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: Jarkko Sakkinen <jarkko@kernel.org> > Cc: Dave Hansen <dave.hansen@linux.intel.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Borislav Petkov <bp@alien8.de> > Cc: x86@kernel.org > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: linux-sgx@vger.kernel.org > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > arch/x86/kernel/cpu/sgx/ioctl.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c > index b65ab214bdf5..4b8f6c9f8ef5 100644 > --- a/arch/x86/kernel/cpu/sgx/ioctl.c > +++ b/arch/x86/kernel/cpu/sgx/ioctl.c > @@ -350,16 +350,18 @@ static int sgx_validate_offset_length(struct sgx_encl *encl, > unsigned long offset, > unsigned long length) > { > + unsigned long sum; > + > if (!IS_ALIGNED(offset, PAGE_SIZE)) > return -EINVAL; > > if (!length || !IS_ALIGNED(length, PAGE_SIZE)) > return -EINVAL; > > - if (offset + length < offset) > + if (check_add_overflow(offset, length, &sum)) > return -EINVAL; > > - if (offset + length - PAGE_SIZE >= encl->size) > + if (sum - PAGE_SIZE >= encl->size) > return -EINVAL; > > return 0; Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> BR, Jarkko
diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c index b65ab214bdf5..4b8f6c9f8ef5 100644 --- a/arch/x86/kernel/cpu/sgx/ioctl.c +++ b/arch/x86/kernel/cpu/sgx/ioctl.c @@ -350,16 +350,18 @@ static int sgx_validate_offset_length(struct sgx_encl *encl, unsigned long offset, unsigned long length) { + unsigned long sum; + if (!IS_ALIGNED(offset, PAGE_SIZE)) return -EINVAL; if (!length || !IS_ALIGNED(length, PAGE_SIZE)) return -EINVAL; - if (offset + length < offset) + if (check_add_overflow(offset, length, &sum)) return -EINVAL; - if (offset + length - PAGE_SIZE >= encl->size) + if (sum - PAGE_SIZE >= encl->size) return -EINVAL; return 0;
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: Jarkko Sakkinen <jarkko@kernel.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: x86@kernel.org Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: linux-sgx@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/x86/kernel/cpu/sgx/ioctl.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)