Re: [PATCH] arm: kasan: clear stale stack poison

[Mark Rutland <mark.rutland@arm.com>]

Hi,

On Fri, Dec 22, 2023 at 10:27:41AM +0800, boy.wu wrote:
> From: Boy Wu <boy.wu@mediatek.com>
> 
> We found below OOB crash:
> 
> [   33.452494] ==================================================================
> [   33.453513] BUG: KASAN: stack-out-of-bounds in refresh_cpu_vm_stats.constprop.0+0xcc/0x2ec
> [   33.454660] Write of size 164 at addr c1d03d30 by task swapper/0/0
> [   33.455515]
> [   33.455767] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G           O       6.1.25-mainline #1
> [   33.456880] Hardware name: Generic DT based system
> [   33.457555]  unwind_backtrace from show_stack+0x18/0x1c
> [   33.458326]  show_stack from dump_stack_lvl+0x40/0x4c
> [   33.459072]  dump_stack_lvl from print_report+0x158/0x4a4
> [   33.459863]  print_report from kasan_report+0x9c/0x148
> [   33.460616]  kasan_report from kasan_check_range+0x94/0x1a0
> [   33.461424]  kasan_check_range from memset+0x20/0x3c
> [   33.462157]  memset from refresh_cpu_vm_stats.constprop.0+0xcc/0x2ec
> [   33.463064]  refresh_cpu_vm_stats.constprop.0 from tick_nohz_idle_stop_tick+0x180/0x53c
> [   33.464181]  tick_nohz_idle_stop_tick from do_idle+0x264/0x354
> [   33.465029]  do_idle from cpu_startup_entry+0x20/0x24
> [   33.465769]  cpu_startup_entry from rest_init+0xf0/0xf4
> [   33.466528]  rest_init from arch_post_acpi_subsys_init+0x0/0x18
> [   33.467397]
> [   33.467644] The buggy address belongs to stack of task swapper/0/0
> [   33.468493]  and is located at offset 112 in frame:
> [   33.469172]  refresh_cpu_vm_stats.constprop.0+0x0/0x2ec
> [   33.469917]
> [   33.470165] This frame has 2 objects:
> [   33.470696]  [32, 76) 'global_zone_diff'
> [   33.470729]  [112, 276) 'global_node_diff'
> [   33.471294]
> [   33.472095] The buggy address belongs to the physical page:
> [   33.472862] page:3cd72da8 refcount:1 mapcount:0 mapping:00000000 index:0x0 pfn:0x41d03
> [   33.473944] flags: 0x1000(reserved|zone=0)
> [   33.474565] raw: 00001000 ed741470 ed741470 00000000 00000000 00000000 ffffffff 00000001
> [   33.475656] raw: 00000000
> [   33.476050] page dumped because: kasan: bad access detected
> [   33.476816]
> [   33.477061] Memory state around the buggy address:
> [   33.477732]  c1d03c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [   33.478630]  c1d03c80: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 00 00
> [   33.479526] >c1d03d00: 00 04 f2 f2 f2 f2 00 00 00 00 00 00 f1 f1 f1 f1
> [   33.480415]                                                ^
> [   33.481195]  c1d03d80: 00 00 00 00 00 00 00 00 00 00 04 f3 f3 f3 f3 f3
> [   33.482088]  c1d03e00: f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
> [   33.482978] ==================================================================
> 
> We find the root cause of this OOB is that arm does not clear stale stack
> poison in the case of cpuidle.
> 
> This patch refer to arch/arm64/kernel/sleep.S to resolve this issue.
> 
> Signed-off-by: Boy Wu <boy.wu@mediatek.com>

It looks like you're specifically referring to what arm64 did in commit:

  0d97e6d8024c71cc ("arm64: kasan: clear stale stack poison")

Where the commit message explained the problem:

| Functions which the compiler has instrumented for KASAN place poison on
| the stack shadow upon entry and remove this poison prior to returning.
| 
| In the case of cpuidle, CPUs exit the kernel a number of levels deep in
| C code.  Any instrumented functions on this critical path will leave
| portions of the stack shadow poisoned.
| 
| If CPUs lose context and return to the kernel via a cold path, we
| restore a prior context saved in __cpu_suspend_enter are forgotten, and
| we never remove the poison they placed in the stack shadow area by
| functions calls between this and the actual exit of the kernel.
| 
| Thus, (depending on stackframe layout) subsequent calls to instrumented
| functions may hit this stale poison, resulting in (spurious) KASAN
| splats to the console.
| 
| To avoid this, clear any stale poison from the idle thread for a CPU
| prior to bringing a CPU online.

... which we then extended to check for CONFIG_KASAN_STACK in commit:

  d56a9ef84bd0e1e8 ("kasan, arm64: unpoison stack only with CONFIG_KASAN_STACK")

If you can fold in the description above (i.e. cite commit 0d97e6d8024c71cc and
a copy of its commit message):

Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
>  arch/arm/kernel/sleep.S | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm/kernel/sleep.S b/arch/arm/kernel/sleep.S
> index a86a1d4f3461..93afd1005b43 100644
> --- a/arch/arm/kernel/sleep.S
> +++ b/arch/arm/kernel/sleep.S
> @@ -127,6 +127,10 @@ cpu_resume_after_mmu:
>  	instr_sync
>  #endif
>  	bl	cpu_init		@ restore the und/abt/irq banked regs
> +#if defined(CONFIG_KASAN) && defined(CONFIG_KASAN_STACK)
> +	mov	r0, sp
> +	bl	kasan_unpoison_task_stack_below
> +#endif
>  	mov	r0, #0			@ return zero on success
>  	ldmfd	sp!, {r4 - r11, pc}
>  ENDPROC(cpu_resume_after_mmu)
> -- 
> 2.18.0
> 
>