| Message ID | 20240123002814.1396804-35-keescook@chromium.org |
|---|---|
| State | New |
| Headers | show |
| Series | None | expand |
On Tue, Jan 23, 2024 at 2:03 AM Kees Cook <keescook@chromium.org> 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: "Rafael J. Wysocki" <rafael@kernel.org> > Cc: Len Brown <lenb@kernel.org> > Cc: linux-acpi@vger.kernel.org > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > drivers/acpi/custom_method.c | 2 +- I may attempt to drop custom_method.c in this cycle, is there a problem if I take this into my tree for now? > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c > index d39a9b474727..0789317f4a1a 100644 > --- a/drivers/acpi/custom_method.c > +++ b/drivers/acpi/custom_method.c > @@ -54,7 +54,7 @@ static ssize_t cm_write(struct file *file, const char __user *user_buf, > > if ((*ppos > max_size) || > (*ppos + count > max_size) || > - (*ppos + count < count) || > + (add_would_overflow(count, *ppos)) || > (count > uncopied_bytes)) { > kfree(buf); > buf = NULL; > -- > 2.34.1 >
On Wed, Jan 24, 2024 at 08:52:48PM +0100, Rafael J. Wysocki wrote: > On Tue, Jan 23, 2024 at 2:03 AM Kees Cook <keescook@chromium.org> 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: "Rafael J. Wysocki" <rafael@kernel.org> > > Cc: Len Brown <lenb@kernel.org> > > Cc: linux-acpi@vger.kernel.org > > Signed-off-by: Kees Cook <keescook@chromium.org> > > --- > > drivers/acpi/custom_method.c | 2 +- > > I may attempt to drop custom_method.c in this cycle, is there a > problem if I take this into my tree for now? The helper doesn't exist in tree yet, but it may be a bit before these refactors land, so if custom_method vanishes before then, that's great! :) -Kees
diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c index d39a9b474727..0789317f4a1a 100644 --- a/drivers/acpi/custom_method.c +++ b/drivers/acpi/custom_method.c @@ -54,7 +54,7 @@ static ssize_t cm_write(struct file *file, const char __user *user_buf, if ((*ppos > max_size) || (*ppos + count > max_size) || - (*ppos + count < count) || + (add_would_overflow(count, *ppos)) || (count > uncopied_bytes)) { kfree(buf); buf = NULL;
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: "Rafael J. Wysocki" <rafael@kernel.org> Cc: Len Brown <lenb@kernel.org> Cc: linux-acpi@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- drivers/acpi/custom_method.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)