Re: [PATCH 0/6 v14] KASan for Arm

[Ard Biesheuvel <ardb@kernel.org>]

On Sun, 4 Oct 2020 at 10:06, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Sat, 3 Oct 2020 at 17:50, Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > On Thu, 1 Oct 2020 at 21:19, Florian Fainelli <f.fainelli@gmail.com> wrote:
> > >
> > >
> > >
> > > On 10/1/2020 8:22 AM, Linus Walleij wrote:
> > > > This is the 14th iteration of KASan for ARM/Aarch32.
> > > >
> > > > I have added one patch in the beginning of the series to
> > > > fix the issue when the DTB (often attached DTB) ends up
> > > > in lowmem. It also amends ARM to copy the device tree
> > > > instead of just unflattening it and using it from where
> > > > it is.
> > > >
> > > > This fixes my particular issue on the Qualcomm APQ8060
> > > > and I hope it may also solve Florian's issue and what
> > > > Ard has been seeing. If you inspect patch 1/6 you can
> > > > see what has been going on for me. My hypothesis about
> > > > what was going on was mostly right.
> > > >
> > > > You are encouraged to test this patch set to find memory out
> > > > of bounds bugs with ARM32 platforms and drivers.
> > > >
> > > > There is a git branch you can pull in:
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-integrator.git/log/?h=kasan
> > >
> > > It does appear to be slight better, although all platforms that I have
> > > where memory starts at physical address 0 cannot boot, attached logs
> > > which are all more or less the same.
> > >
> > > The physical memory map looks like this:
> > >
> > > 0..3GB -> DRAM
> > > 3GB..4GB -> Registers, Boot ROM, Boot SRAM
> > > 4GB..12GB -> DRAM extension
> > >
> > > Do any of the platforms you use for testing have a similar memory map?
> > > Could you try to contrive a QEMU machine to have something similar in
> > > case that helps reproducing these failures?
> > >
> >
> > I am getting very similar failures on a Raspberry Pi4 booting in
> > 32-bit mode from U-boot+EFI
> >
> > Full log attached.
> >
> > I will try to dig a bit deeper.
>
> OK, one obvious issue with the code as-is is that the following routine
>
> static __init void *kasan_alloc_block(size_t size)
> {
>   return memblock_alloc_try_nid(size, size, __pa(MAX_DMA_ADDRESS),
>                                 MEMBLOCK_ALLOC_KASAN, NUMA_NO_NODE);
> }
>
> is called after the early shadow is unmapped, but before the permanent
> shadow is in place. memblock_alloc_try_nid() clears the newly
> allocated memory using memset(), which checks the associated shadow,
> which is unmapped -> BOOM.
>
> With the following implementation, I can avoid the crash similar to
> the one Florian is reporting:
>
> static __init void *kasan_alloc_block(size_t size)
> {
>   void *p = memblock_alloc_try_nid_raw(size, size,
>     __pa(MAX_DMA_ADDRESS), MEMBLOCK_ALLOC_KASAN,
>     NUMA_NO_NODE);
>
>   if (p)
>     __memset(p, 0, size);
>   return p;
> }
>
> However, I still get a hang a bit later, and I haven't tracked that down yet.

The above issue appears to be related to TLB maintenance. So keeping
kasan_alloc_block() as is, and doing

--- a/arch/arm/mm/kasan_init.c
+++ b/arch/arm/mm/kasan_init.c
@@ -223,6 +223,8 @@ void __init kasan_init(void)
                __pgd(__pa(tmp_pmd_table) | PMD_TYPE_TABLE | L_PGD_SWAPPER));
 #endif
        cpu_switch_mm(tmp_pgd_table, &init_mm);
+       local_flush_tlb_all();
+
        clear_pgds(KASAN_SHADOW_START, KASAN_SHADOW_END);

        kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),

instead fixes the crash as well.

Still have the hang right after though ..

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