linux-kernel - Re: BUG: KASAN: global-out-of-bounds in unmap_kernel_at

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Date:   Sun, 22 Apr 2018 20:06:39 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Jan Kiszka <jan.kiszka@....de>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        will.deacon@....com, catalin.marinas@....com,
        suzuki.poulose@....com
Subject: Re: BUG: KASAN: global-out-of-bounds in
 unmap_kernel_at_el0+0x70/0x1a0

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@....com>
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@....com>
Reported-by: Jan Kiszka <jan.kiszka@....de>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>
Cc: Will Deacon <will.deacon@....com>
---
 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";
 
-- 
2.11.0