linux-kernel - Re: [PATCH v2] x86/kexec: Add EFI config table identity mapping for kexec kernel

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Message-ID: <20230717141409.GGZLVMsU6d/9mpJvMO@fat_crate.local>
Date:   Mon, 17 Jul 2023 16:14:09 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Tao Liu <ltao@...hat.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, ardb@...nel.org,
        linux-kernel@...r.kernel.org, bhe@...hat.com, dyoung@...hat.com,
        kexec@...ts.infradead.org, linux-efi@...r.kernel.org
Subject: Re: [PATCH v2] x86/kexec: Add EFI config table identity mapping for
 kexec kernel

On Mon, Jul 17, 2023 at 09:53:06PM +0800, Tao Liu wrote:
> ...snip...
> [   21.360763]  nvme0n1: p1 p2 p3
> [   21.364207] igc 0000:03:00.0: PTM enabled, 4ns granularity
> [   21.421097] pps pps1: new PPS source ptp1
> [   21.425396] igc 0000:03:00.0 (unnamed net_device) (uninitialized): PHC added
> [   21.457005] igc 0000:03:00.0: 4.000 Gb/s available PCIe bandwidth
> (5.0 GT/s PCIe x1 link)
> [   21.465210] igc 0000:03:00.0 eth1: MAC: ...snip...
> [   21.473424] igc 0000:03:00.0 enp3s0: renamed from eth1
> [   21.479446] BUG: kernel NULL pointer dereference, address: 0000000000000008
> [   21.486405] #PF: supervisor read access in kernel mode
> [   21.491519] mmc1: Failed to initialize a non-removable card
> [   21.491538] #PF: error_code(0x0000) - not-present page
> [   21.502229] PGD 0 P4D 0
> [   21.504773] Oops: 0000 [#1] PREEMPT SMP NOPTI
> [   21.509133] CPU: 3 PID: 402 Comm: systemd-udevd Not tainted 6.5.0-rc1+ #1
> [   21.515905] Hardware name: ...snip...
> [   21.522851] RIP: 0010:kernfs_dop_revalidate+0x2b/0x120

So something's weird here - my patch should not cause a null ptr deref
here.

> [   21.527995] Code: 1f 44 00 00 83 e6 40 0f 85 07 01 00 00 41 55 41
> 54 55 53 48 8b 47 30 48 89 fb 48 85 c0 0f 84 a2 00 00 00 48 8b a87

This looks weird too. There's no "<>" brackets denoting which byte it
was exactly where RIP pointed to when the NULL ptr happened.

Do

make fs/kernfs/dir.s

and upload dir.s and the dir.o file somewhere.

In any case, my patch shouldn't be causing this. At least I don't see
it.

I'm testing a better version of the patch and it should not cause this
thing even less.

> The stack trace may not be the same all the time, I didn't dive deep
> into the root cause, but it looks to me the patch will cause an
> unknown issue. Also I tested the patch on kernel-5.14.0-318.el9, it

This is the upstream kernel mailing list so those Frankenstein kernels
are all left to you.

Good luck. :-)

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette