linux-kernel - Re: [PATCH 1/2] kfence: add function to mask address bits

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Message-ID: <CANpmjNPAS5kDsADb-DwvdFR9nRnX47-mFuEG2vmMPn5U3i3sGQ@mail.gmail.com>
Date:   Fri, 14 May 2021 13:23:33 +0200
From:   Marco Elver <elver@...gle.com>
To:     Sven Schnelle <svens@...ux.ibm.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH 1/2] kfence: add function to mask address bits

On Fri, 14 May 2021 at 13:03, Sven Schnelle <svens@...ux.ibm.com> wrote:
>
> Marco Elver <elver@...gle.com> writes:
>
> >> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> >> index e18fbbd5d9b4..bc15e3cb71d5 100644
> >> --- a/mm/kfence/core.c
> >> +++ b/mm/kfence/core.c
> >> @@ -50,6 +50,11 @@ static unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE
> >>  #endif
> >>  #define MODULE_PARAM_PREFIX "kfence."
> >>
> >> +unsigned long __weak kfence_arch_mask_addr(unsigned long addr)
> >> +{
> >> +       return addr;
> >> +}
> >
> > I don't think this belongs here, because it's test-specific,
> > furthermore if possible we'd like to put all arch-specific code into
> > <asm/kfence.h> (whether or not your arch will have 'static inline'
> > functions only, like x86 and arm64, or not is up to you).
> >
> > Because I don't see this function being terribly complex, also let's
> > just make it a macro.
> >
> > Then in kfence_test.c, we can have:
> >
> > #ifndef kfence_test_mask_address
> > #define kfence_test_mask_address(addr) (addr)
> > #endif
> >
> > and then have it include <asm/kfence.h>. And in your <asm/kfence.h>
> > you can simply say:
> >
> > #define kfence_test_mask_address(addr) (.........)
> >
> > It also avoids having to export kfence_test_mask_address, because
> > kfence_test can be built as a module.
>
> Ok, i'll change my patch accordingly. Thanks!

Sounds good. Also please add a brief comment on top of the
"kfence_test_mask_address" part in kfence_test, like "/* May be
overridden by <asm/kfence.h>. */" -- we have something similar in
mm/kfence/report.c. Also, I think we want to call the macro
"arch_kfence_test_address" -- the "mask" part is very much
arch-dependent, and might not even be a mask on some other weird
hypothetical architecture.

Thanks,
-- Marco