| Message ID | 20240123002814.1396804-38-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | overflow: Refactor open-coded arithmetic wrap-around | expand |
The commit title is odd here; '3117/1' is the patch tracker name for the last patch. The title should probably be: arm: nwfpe: Refactor intentional wrap-around test Mark. On Mon, Jan 22, 2024 at 04:27:13PM -0800, 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 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: Russell King <linux@armlinux.org.uk> > Cc: linux-arm-kernel@lists.infradead.org > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > arch/arm/nwfpe/softfloat.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm/nwfpe/softfloat.c b/arch/arm/nwfpe/softfloat.c > index ffa6b438786b..0635b1eda1d3 100644 > --- a/arch/arm/nwfpe/softfloat.c > +++ b/arch/arm/nwfpe/softfloat.c > @@ -603,7 +603,7 @@ static floatx80 > roundBits = zSig0 & roundMask; > if ( 0x7FFD <= (bits32) ( zExp - 1 ) ) { > if ( ( 0x7FFE < zExp ) > - || ( ( zExp == 0x7FFE ) && ( zSig0 + roundIncrement < zSig0 ) ) > + || ( ( zExp == 0x7FFE ) && (add_would_overflow(zSig0, roundIncrement)) ) > ) { > goto overflow; > } > -- > 2.34.1 > >
On Tue, Jan 23, 2024 at 09:56:22AM +0000, Mark Rutland wrote: > The commit title is odd here; '3117/1' is the patch tracker name for the last > patch. The title should probably be: > > arm: nwfpe: Refactor intentional wrap-around test Whoops, yes. I need to teach my prefix-guessing script to drop the ARM patch tracker numbers... -Kees > > Mark. > > On Mon, Jan 22, 2024 at 04:27:13PM -0800, 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 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: Russell King <linux@armlinux.org.uk> > > Cc: linux-arm-kernel@lists.infradead.org > > Signed-off-by: Kees Cook <keescook@chromium.org> > > --- > > arch/arm/nwfpe/softfloat.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/arm/nwfpe/softfloat.c b/arch/arm/nwfpe/softfloat.c > > index ffa6b438786b..0635b1eda1d3 100644 > > --- a/arch/arm/nwfpe/softfloat.c > > +++ b/arch/arm/nwfpe/softfloat.c > > @@ -603,7 +603,7 @@ static floatx80 > > roundBits = zSig0 & roundMask; > > if ( 0x7FFD <= (bits32) ( zExp - 1 ) ) { > > if ( ( 0x7FFE < zExp ) > > - || ( ( zExp == 0x7FFE ) && ( zSig0 + roundIncrement < zSig0 ) ) > > + || ( ( zExp == 0x7FFE ) && (add_would_overflow(zSig0, roundIncrement)) ) > > ) { > > goto overflow; > > } > > -- > > 2.34.1 > > > >
diff --git a/arch/arm/nwfpe/softfloat.c b/arch/arm/nwfpe/softfloat.c index ffa6b438786b..0635b1eda1d3 100644 --- a/arch/arm/nwfpe/softfloat.c +++ b/arch/arm/nwfpe/softfloat.c @@ -603,7 +603,7 @@ static floatx80 roundBits = zSig0 & roundMask; if ( 0x7FFD <= (bits32) ( zExp - 1 ) ) { if ( ( 0x7FFE < zExp ) - || ( ( zExp == 0x7FFE ) && ( zSig0 + roundIncrement < zSig0 ) ) + || ( ( zExp == 0x7FFE ) && (add_would_overflow(zSig0, roundIncrement)) ) ) { goto overflow; }
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: Russell King <linux@armlinux.org.uk> Cc: linux-arm-kernel@lists.infradead.org Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/arm/nwfpe/softfloat.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)