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    SubjectRe: [PATCH 35/82] ACPI: custom_method: Refactor intentional wrap-around test
    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

    --
    Kees Cook

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