Re: BUG: KASAN: global-out-of-bounds in unmap_kernel_at_el0+0x70/0x1a0

[Jan Kiszka]

On 2018-04-22 21:06, Mark Rutland wrote:
> On Sun, Apr 22, 2018 at 12:47:57PM +0200, Jan Kiszka wrote:
>> Hi,
>>
>> this can be triggered simply by running
>>
>> # echo 0 > /sys/devices/system/cpu/cpu3/online
>> # echo 1 > /sys/devices/system/cpu/cpu3/online
>>
>> [  455.904854] ==================================================================
>> [  455.906108] BUG: KASAN: global-out-of-bounds in unmap_kernel_at_el0+0x70/0x1a0
>> [  455.906668] Read of size 4 at addr ffff200008e3a9d8 by task swapper/3/0
> 
> It looks like we miss a sentinel in kpti_safe_list.
> 
> Does the below help?
> 
> Mark.
> 
> ---->8----
> From ade322407e3d6d1f50e558ebd50d2c1c7bd811c2 Mon Sep 17 00:00:00 2001
> From: Mark Rutland <mark.rutland@xxxxxxx>
> Date: Sun, 22 Apr 2018 19:58:08 +0100
> Subject: [PATCH] arm64: add sentinel to kpti_safe_list
> 
> We're missing a sentinel entry in kpti_safe_list. Thus is_midr_in_range_list()
> can walk past the end of kpti_safe_list. Depending on the contents of memory,
> this could erroneously match a CPU's MIDR, cause a data abort, or other bad
> outcomes.
> 
> Add the sentinel entry to avoid this.
> 
> Fixes: be5b299830c63ed7 ("arm64: capabilities: Add support for checks based on a list of MIDRs")
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Reported-by: Jan Kiszka <jan.kiszka@xxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> ---
>  arch/arm64/kernel/cpufeature.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 536d572e5596..9d1b06d67c53 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -868,6 +868,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
>  	static const struct midr_range kpti_safe_list[] = {
>  		MIDR_ALL_VERSIONS(MIDR_CAVIUM_THUNDERX2),
>  		MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
> +		{ /* sentinel */ }
>  	};
>  	char const *str = "command line option";
>  
> 

Jep, all fine now!

Jan

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