On Sun, 4 Oct 2020 at 10:06, Ard Biesheuvel [off-list ref] wrote:

On Sat, 3 Oct 2020 at 17:50, Ard Biesheuvel [off-list ref] wrote:

quoted

On Thu, 1 Oct 2020 at 21:19, Florian Fainelli [off-list ref] wrote:

quoted

On 10/1/2020 8:22 AM, Linus Walleij wrote:

quoted

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 ..

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel