Re: [PATCH 1/2] riscv: Fix asan-stack clang build

[Alexandre Ghiti]

On Thu, Oct 28, 2021 at 8:45 AM Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote:
>
> On Wed, 27 Oct 2021 22:34:32 PDT (-0700), alexandre.ghiti@xxxxxxxxxxxxx wrote:
> > On Thu, Oct 28, 2021 at 7:30 AM Alexandre Ghiti
> > <alexandre.ghiti@xxxxxxxxxxxxx> wrote:
> >>
> >> On Thu, Oct 28, 2021 at 7:02 AM Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote:
> >> >
> >> > On Wed, 27 Oct 2021 21:15:28 PDT (-0700), alexandre.ghiti@xxxxxxxxxxxxx wrote:
> >> > > On Thu, Oct 28, 2021 at 1:06 AM Palmer Dabbelt <palmer@xxxxxxxxxxx> wrote:
> >> > >>
> >> > >> On Tue, 26 Oct 2021 21:58:42 PDT (-0700), alexandre.ghiti@xxxxxxxxxxxxx wrote:
> >> > >> > Nathan reported that because KASAN_SHADOW_OFFSET was not defined in
> >> > >> > Kconfig, it prevents asan-stack from getting disabled with clang even
> >> > >> > when CONFIG_KASAN_STACK is disabled: fix this by defining the
> >> > >> > corresponding config.
> >> > >> >
> >> > >> > Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> >> > >> > Signed-off-by: Alexandre Ghiti <alexandre.ghiti@xxxxxxxxxxxxx>
> >> > >> > ---
> >> > >> >  arch/riscv/Kconfig             | 6 ++++++
> >> > >> >  arch/riscv/include/asm/kasan.h | 3 +--
> >> > >> >  arch/riscv/mm/kasan_init.c     | 3 +++
> >> > >> >  3 files changed, 10 insertions(+), 2 deletions(-)
> >> > >> >
> >> > >> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> >> > >> > index c1abbc876e5b..79250b1ed54e 100644
> >> > >> > --- a/arch/riscv/Kconfig
> >> > >> > +++ b/arch/riscv/Kconfig
> >> > >> > @@ -162,6 +162,12 @@ config PAGE_OFFSET
> >> > >> >       default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
> >> > >> >       default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
> >> > >> >
> >> > >> > +config KASAN_SHADOW_OFFSET
> >> > >> > +     hex
> >> > >> > +     depends on KASAN_GENERIC
> >> > >> > +     default 0xdfffffc800000000 if 64BIT
> >> > >> > +     default 0xffffffff if 32BIT
> >> > >>
> >> > >> I thought I posted this somewhere, but this is exactly what my first
> >> > >> guess was.  The problem is that it's hanging on boot for me.  I don't
> >> > >> really have anything exotic going on, it's just a defconfig with
> >> > >> CONFIG_KASAN=y running in QEMU.
> >> > >>
> >> > >> Does this boot for you?
> >> > >
> >> > > Yes with the 2nd patch of this series which fixes the issue
> >> > > encountered here. And that's true I copied/pasted this part of your
> >> > > patch which was better than what I had initially done, sorry I should
> >> > > have mentioned you did that, please add a Codeveloped-by or something
> >> > > like that.
>
> OK, those should probably be in the opposite order (though it looks like
> they're inter-dependent, which makes things a bit trickier).
>
> >> >
> >> > Not sure if I'm missing something, but it's still not booting for me.
> >> > I've put what I'm testing on palmer/to-test, it's these two on top of
> >> > fixes and merged into Linus' tree
> >> >
> >> >     *   6d7d351902ff - (HEAD -> to-test, palmer/to-test) Merge remote-tracking branch 'palmer/fixes' into to-test (7 minutes ago) <Palmer Dabbelt>
> >> >     |\
> >> >     | * 782551edf8f8 - (palmer/fixes) riscv: Fix CONFIG_KASAN_STACK build (6 hours ago) <Alexandre Ghiti>
> >> >     | * 47383e5b3c4f - riscv: Fix asan-stack clang build (6 hours ago) <Alexandre Ghiti>
> >> >     | * 64a19591a293 - (riscv/fixes) riscv: fix misalgned trap vector base address (9 hours ago) <Chen Lu>
> >> >     * |   1fc596a56b33 - (palmer/master, linus/master, linus/HEAD, master) Merge tag 'trace-v5.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace (11 hours ago) <Linus Torvalds>
> >> >
> >> > Am I missing something else?
> >>
> >> Hmm, that's weird, I have just done the same: cherry-picked both my
> >> commits on top of fixes (64a19591a293) and it boots fine with KASAN
> >> enabled. Maybe a config thing? I pushed my branch here:
> >> https://github.com/AlexGhiti/riscv-linux/tree/int/alex/kasan_stack_fixes_rebase
> >
> > I pushed the config I use and that boots in that branch, maybe there's
> > another issue somewhere.
>
> CONFIG_KASAN_VMALLOC=n is what's causing the failure.  I'm testing both
> polarities of that, looks like your config has =y.  I haven't looked any
> further as I'm pretty much cooked for tonight, but if you don't have
> time then I'll try to find some time tomorrow.
>

Arf, that was obvious and just under my nose: without KASAN_VMALLOC,
kasan_populate_early_shadow is called and creates the same issue that
the second patch fixes.

I'll send a v2 today and try to swap both patches to avoid having a
non-bootable kernel commit.

Alex

> >
> >>
> >> >
> >> > >
> >> > > Thanks,
> >> > >
> >> > > Alex
> >> > >
> >> > >>
> >> > >> > +
> >> > >> >  config ARCH_FLATMEM_ENABLE
> >> > >> >       def_bool !NUMA
> >> > >> >
> >> > >> > diff --git a/arch/riscv/include/asm/kasan.h b/arch/riscv/include/asm/kasan.h
> >> > >> > index a2b3d9cdbc86..b00f503ec124 100644
> >> > >> > --- a/arch/riscv/include/asm/kasan.h
> >> > >> > +++ b/arch/riscv/include/asm/kasan.h
> >> > >> > @@ -30,8 +30,7 @@
> >> > >> >  #define KASAN_SHADOW_SIZE    (UL(1) << ((CONFIG_VA_BITS - 1) - KASAN_SHADOW_SCALE_SHIFT))
> >> > >> >  #define KASAN_SHADOW_START   KERN_VIRT_START
> >> > >> >  #define KASAN_SHADOW_END     (KASAN_SHADOW_START + KASAN_SHADOW_SIZE)
> >> > >> > -#define KASAN_SHADOW_OFFSET  (KASAN_SHADOW_END - (1ULL << \
> >> > >> > -                                     (64 - KASAN_SHADOW_SCALE_SHIFT)))
> >> > >> > +#define KASAN_SHADOW_OFFSET  _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
> >> > >> >
> >> > >> >  void kasan_init(void);
> >> > >> >  asmlinkage void kasan_early_init(void);
> >> > >> > diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
> >> > >> > index d7189c8714a9..8175e98b9073 100644
> >> > >> > --- a/arch/riscv/mm/kasan_init.c
> >> > >> > +++ b/arch/riscv/mm/kasan_init.c
> >> > >> > @@ -17,6 +17,9 @@ asmlinkage void __init kasan_early_init(void)
> >> > >> >       uintptr_t i;
> >> > >> >       pgd_t *pgd = early_pg_dir + pgd_index(KASAN_SHADOW_START);
> >> > >> >
> >> > >> > +     BUILD_BUG_ON(KASAN_SHADOW_OFFSET !=
> >> > >> > +             KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT)));
> >> > >> > +
> >> > >> >       for (i = 0; i < PTRS_PER_PTE; ++i)
> >> > >> >               set_pte(kasan_early_shadow_pte + i,
> >> > >> >                       mk_pte(virt_to_page(kasan_early_shadow_page),