linux-kernel - Re: [RFC PATCH] x86/msr: Filter MSR writes

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Date:   Fri, 12 Jun 2020 21:47:53 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86/msr: Filter MSR writes

On Fri, Jun 12, 2020 at 07:48:01PM +0200, Borislav Petkov wrote:
> > So the first phase might be to introduce this, but have the default
> > for non-recognized MSR's be "log", not "deny".
> 
> Ok. How are we going to "learn" about those non-recognized MSRs? Ask
> people to send us a note to lkml so that we can fix the list once they
> see the logged message?

We could do something noisy like this:

[   27.395795] msr: filter_write: Write to unrecognized MSR 0x10
[   27.396865] msr: Please report to x86@...nel.org
[   27.397811] ------------[ cut here ]------------
[   27.398630] WARNING: CPU: 10 PID: 4405 at arch/x86/kernel/msr.c:83 msr_write.cold+0x1f/0x26 [msr]
[   27.400123] Modules linked in: msr
[   27.400728] CPU: 10 PID: 4405 Comm: wrmsr Not tainted 5.7.0+ #2
[   27.400838] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
[   27.400838] RIP: 0010:msr_write.cold+0x1f/0x26 [msr]
[   27.400838] Code: eb e0 49 c7 c4 ea ff ff ff eb d7 48 c7 c6 40 11 00 a0 48 c7 c7 c0 10 00 a0 e8 5f 83 0c e1 48 c7 c7 f0 10 00 a0 e8 53 83 0c e1 <0f> 0b e9 af fe ff ff 8b 3d 7c 20 00 00 be 01 00 00 00 e8 1e c7 06
[   27.400838] RSP: 0018:ffffc900003d7e98 EFLAGS: 00010282
[   27.400838] RAX: 0000000000000024 RBX: 0000000000000008 RCX: 0000000000000007
[   27.400838] RDX: 0000000000000007 RSI: 0000000000000082 RDI: ffff88807dc98360
[   27.400838] RBP: 00007fffffffe978 R08: 00000000000001ca R09: 0000000000000000
[   27.400838] R10: ffffffff82549708 R11: ffffc900003d7d50 R12: 0000000000000008
[   27.400838] R13: 0000000000000000 R14: 0000000000000010 R15: 0000000000000000
[   27.400838] FS:  00007ffff7fb7540(0000) GS:ffff88807dc80000(0000) knlGS:0000000000000000
[   27.400838] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   27.400838] CR2: 00007ffff7e672a0 CR3: 0000000078a4c000 CR4: 00000000003406e0
[   27.400838] Call Trace:
[   27.400838]  vfs_write+0xe4/0x1e0
[   27.400838]  ksys_pwrite64+0x7d/0xb0
[   27.400838]  do_syscall_64+0x48/0x140
[   27.400838]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   27.400838] RIP: 0033:0x7ffff7edda37
[   27.400838] Code: ff ff eb b6 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 8d 05 c9 7c 0d 00 49 89 ca 8b 00 85 c0 75 10 b8 12 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 59 c3 41 55 49 89 cd 41 54 49 89 d4 55 48 89
[   27.400838] RSP: 002b:00007fffffffe968 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
[   27.400838] RAX: ffffffffffffffda RBX: 00007fffffffeb78 RCX: 00007ffff7edda37
[   27.400838] RDX: 0000000000000008 RSI: 00007fffffffe978 RDI: 0000000000000003
[   27.400838] RBP: 0000000000000003 R08: 00007fffffffedb6 R09: 0000000000000000
[   27.400838] R10: 0000000000000010 R11: 0000000000000246 R12: 00007fffffffeb78
[   27.400838] R13: 0000000000000010 R14: 0000000000000000 R15: 0000000000000010
[   27.400838] ---[ end trace 3bd374c0e61187b1 ]---

-- 
Regards/Gruss,
    Boris.

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