linux-kernel - Re: [PATCH] ARC: fix CONFIG_HARDENED

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Message-ID: <53daee07-9c5b-9cf9-f08a-524afaee762a@synopsys.com>
Date:   Thu, 10 Jun 2021 18:56:48 +0000
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Kees Cook <keescook@...omium.org>
CC:     "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Evgeniy Didin <Evgeniy.Didin@...opsys.com>
Subject: Re: [PATCH] ARC: fix CONFIG_HARDENED_USERCOPY

On 6/10/21 10:02 AM, Kees Cook wrote:
> On Wed, Jun 09, 2021 at 03:12:11PM -0700, Vineet Gupta wrote:
>> Currently enabling this triggers a warning
>>
>> | usercopy: Kernel memory overwrite attempt detected to kernel text (offset 155633, size 11)!
>> | usercopy: BUG: failure at mm/usercopy.c:99/usercopy_abort()!
>> |
>> |gcc generated __builtin_trap
>> |Path: /bin/busybox
>> |CPU: 0 PID: 84 Comm: init Not tainted 5.4.22
>> |
>> |[ECR ]: 0x00090005 => gcc generated __builtin_trap
>> |[EFA ]: 0x9024fcaa
>> |[BLINK ]: usercopy_abort+0x8a/0x8c
>> |[ERET ]: memfd_fcntl+0x0/0x470
>> |[STAT32]: 0x80080802 : IE K
>> |BTA: 0x901ba38c SP: 0xbe161ecc FP: 0xbf9fe950
>> |LPS: 0x90677408 LPE: 0x9067740c LPC: 0x00000000
>> |r00: 0x0000003c r01: 0xbf0ed280 r02: 0x00000000
>> |r03: 0xbe15fa30 r04: 0x00d2803e r05: 0x00000000
>> |r06: 0x675d7000 r07: 0x00000000 r08: 0x675d9c00
>> |r09: 0x00000000 r10: 0x0000035c r11: 0x61206572
>> |r12: 0x9024fcaa r13: 0x0000000b r14: 0x0000000b
>> |r15: 0x00000000 r16: 0x90169ffc r17: 0x90168000
>> |r18: 0x00000000 r19: 0xbf092010 r20: 0x00000001
>> |r21: 0x00000011 r22: 0x5ffffff1 r23: 0x90169ff1
>> |r24: 0xbe196c00 r25: 0xbf0ed280
>> |
>> |Stack Trace:
>> | memfd_fcntl+0x0/0x470
>> | usercopy_abort+0x8a/0x8c
>> | __check_object_size+0x10e/0x138
>> | copy_strings+0x1f4/0x38c
>> | __do_execve_file+0x352/0x848
>> | EV_Trap+0xcc/0xd0
> What was the root cause here? Was it that the init section gets freed
> and reused for kmalloc?

Right. ARC _stext was encompassing the init section (to cover the init 
code) so when init gets freed and used by kmalloc, 
check_kernel_text_object() trips as it thinks the allocated pointer is 
in kernel .text. Actually I should have added this to changelog.

Thx,
-Vineet