linux-kernel - Re: [PATCH 0/2] arm64: fix crash when reading /proc/kcore

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Message-ID: <20170609100029.GC10665@leverpostej>
Date:   Fri, 9 Jun 2017 11:00:30 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        jolsa@...nel.org, mingo@...nel.org, akpm@...ux-foundation.org,
        zhongjiang@...wei.com, labbott@...oraproject.org
Subject: Re: [PATCH 0/2] arm64: fix crash when reading /proc/kcore

On Thu, Jun 08, 2017 at 07:41:37PM +0000, Ard Biesheuvel wrote:
> This is a follow-up to patches from zhonjiang [0] and myself [1] that aim
> to solve a problem in the kcore code, which gets confused by the presence
> of block mappings in the vmalloc region.
> 
> While fixing the crash is quite straight forward [2], we need to tweak
> the kcore code itself to ensure that it operates correctly on arm64.
> Fortunately, we can achieve this with two very simple changes:
> 
> - replace a call to is_vmalloc_or_module_addr() in read_kcore() with a
>   comparison of the kclist type field (#1)
> - enable CONFIG_ARCH_PROC_KCORE_TEXT for arm64 (#2)

FWIW, I gave this a spin on a Juno R1 board, and can confirm this
prevents the crash one could previously trigger with:

# cat /proc/kcore > /dev/null

FWIW, for the series:

Acked-by: Mark Rutland <mark.rutland@....com>
Tested-by: Mark Rutland <mark.rutland@....com>

Prior to these patches, I'd get a splat after a couple of seconds, as
below.

Thanks,
Mark.

root@...bensteg:/home/nanook# cat /proc/kcore  > /dev/null
[   44.923557] Unable to handle kernel paging request at virtual address ffffa3a379000000
[   44.931437] pgd = ffff800975e84000
[   44.934832] [ffffa3a379000000] *pgd=0000000000000000
[   44.939772] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[   44.945295] Modules linked in:
[   44.948328] CPU: 4 PID: 2190 Comm: cat Not tainted 4.12.0-rc4-00006-gc50d1fe #2
[   44.955573] Hardware name: ARM Juno development board (r1) (DT)
[   44.961441] task: ffff80097658e800 task.stack: ffff8009748bc000
[   44.967316] PC is at __memcpy+0x100/0x180
[   44.971294] LR is at vread+0x13c/0x260
[   44.975009] pc : [<ffff00000839fe00>] lr : [<ffff0000081be1fc>] pstate: 20000145
[   44.982340] sp : ffff8009748bfca0
[   44.985623] x29: ffff8009748bfca0 x28: ffff80097560f000 
[   44.990892] x27: ffff80097658e800 x26: ffff800977801380 
[   44.996162] x25: 0000000000001000 x24: ffff000008201000 
[   45.001431] x23: 0000000000001000 x22: ffff80097560f000 
[   45.006700] x21: ffff000008e8aa88 x20: ffff000008201000 
[   45.011980] x19: 0000000000001000 x18: 0000ffffeac5f340 
[   45.017259] x17: 0000ffff961def30 x16: ffff0000081fb098 
[   45.022537] x15: 0000ffff96268588 x14: 0000000000000000 
[   45.027815] x13: 0000000000000000 x12: 0000000000000000 
[   45.033094] x11: 0000000000000000 x10: 0000000000000000 
[   45.038372] x9 : 0000000000000000 x8 : 0000000000000000 
[   45.043649] x7 : 0000000000000000 x6 : ffff80097560f000 
[   45.048928] x5 : ffff8009778013b0 x4 : 0000000000000000 
[   45.054206] x3 : 0400000000000001 x2 : 0000000000000f80 
[   45.059484] x1 : ffffa3a379000000 x0 : ffff80097560f000 
[   45.064764] Process cat (pid: 2190, stack limit = 0xffff8009748bc000)
[   45.071158] Stack: (0xffff8009748bfca0 to 0xffff8009748c0000)
[   45.076866] fca0: ffff8009748bfd20 ffff00000826d848 ffff000008fb7958 000000000000d000
[   45.084651] fcc0: 0000000000f5b000 ffff000008fb7948 ffff8009748bfeb8 0000000000003000
[   45.092435] fce0: ffff80097658e800 ffff000008201000 ffff000008e8ff70 0000000000001000
[   45.100219] fd00: ffff8009748bfeb8 0000000000001000 ffff80097560f000 0000000000001000
[   45.108004] fd20: ffff8009748bfdb0 ffff00000825fd30 ffff80097643dc00 fffffffffffffffb
[   45.115788] fd40: 0000000000f58000 ffff8009748bfeb8 0000000060000000 0000000000000015
[   45.123572] fd60: 0000000000000124 000000000000003f ffff000008952000 ffff80097658e800
[   45.131356] fd80: 0000000000000124 ffff80097658e800 ffff80097658e800 ffff80097560f000
[   45.139140] fda0: 0000000376521100 0000000000002000 ffff8009748bfdd0 ffff0000081f8924
[   45.146924] fdc0: 0000000000010000 ffff800976521900 ffff8009748bfe50 ffff0000081f9bf0
[   45.154709] fde0: 0000000000010000 ffff800976521900 0000000060000000 ffff0000081f9ae4
[   45.162493] fe00: ffff8009748bfe30 ffff0000081f9ae4 ffff800976521900 0000000000000000
[   45.170277] fe20: 0000000000f58000 ffff8009748bfeb8 ffff8009748bfe50 ffff0000081f9bcc
[   45.178062] fe40: 0000000000010000 ffff800976521900 ffff8009748bfe80 ffff0000081fb0dc
[   45.185846] fe60: ffff800976521900 ffff800976521900 0000000000f58000 0000000000010000
[   45.193630] fe80: 0000000000000000 ffff000008082f30 0000000000000000 0000800977159000
[   45.201415] fea0: ffffffffffffffff 0000ffff961def4c 0000000000000124 0000000008203000
[   45.209199] fec0: 0000000000000003 0000000000f58000 0000000000010000 0000000000000000
[   45.216983] fee0: 0000000000011011 0000000000000001 0000000000000011 0000000000000002
[   45.224766] ff00: 000000000000003f ff53424451514e42 00000000ffffffff 0000000000000030
[   45.232550] ff20: 0000000000000038 0000000000000000 0000ffff96121a94 0000ffff96268588
[   45.240334] ff40: 0000000000000000 0000ffff961def30 0000ffffeac5f340 0000000000010000
[   45.248118] ff60: 000000000041a310 0000000000f58000 0000000000000003 000000007fffe000
[   45.255901] ff80: 00000000004088d0 0000000000010000 0000000000000000 0000000000000000
[   45.263685] ffa0: 0000000000010000 0000ffffeac5f610 0000000000404dcc 0000ffffeac5f610
[   45.271469] ffc0: 0000ffff961def4c 0000000060000000 0000000000000003 000000000000003f
[   45.279252] ffe0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[   45.287032] Call trace:
[   45.289466] Exception stack(0xffff8009748bfad0 to 0xffff8009748bfc00)
[   45.295861] fac0:                                   0000000000001000 0001000000000000
[   45.303645] fae0: ffff8009748bfca0 ffff00000839fe00 ffff8009748bfb20 ffff0000080eca80
[   45.311429] fb00: ffff8009748bfb20 ffff0000080ff95c 0000000000000000 0000000000000025
[   45.319213] fb20: ffff8009748bfb50 ffff0000080eca80 ffff80097658e800 00000000000019a0
[   45.326997] fb40: ffff80097658e800 0000000000000001 ffff8009748bfb70 ffff0000080edbbc
[   45.334782] fb60: ffff8009748bfb70 ffff0000080edbd0 ffff80097560f000 ffffa3a379000000
[   45.342566] fb80: 0000000000000f80 0400000000000001 0000000000000000 ffff8009778013b0
[   45.350349] fba0: ffff80097560f000 0000000000000000 0000000000000000 0000000000000000
[   45.358132] fbc0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[   45.365916] fbe0: 0000000000000000 0000ffff96268588 ffff0000081fb098 0000ffff961def30
[   45.373701] [<ffff00000839fe00>] __memcpy+0x100/0x180
[   45.378721] [<ffff00000826d848>] read_kcore+0x280/0x3b8
[   45.383914] [<ffff00000825fd30>] proc_reg_read+0x60/0x90
[   45.389193] [<ffff0000081f8924>] __vfs_read+0x1c/0x108
[   45.394299] [<ffff0000081f9bf0>] vfs_read+0x80/0x130
[   45.399233] [<ffff0000081fb0dc>] SyS_read+0x44/0xa0
[   45.404082] [<ffff000008082f30>] el0_svc_naked+0x24/0x28
[   45.409360] Code: d503201f d503201f d503201f d503201f (a8c12027) 
[   45.415467] ---[ end trace 1e058edb915b6297 ]---
[   45.420080] note: cat[2190] exited with preempt_count 2