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

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Date:   Mon, 17 Jul 2023 22:24:32 +0800
From:   Tao Liu <ltao@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
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 10:14 PM Borislav Petkov <bp@...en8.de> wrote:
>
> 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.
>
OK, thanks for the help. I will re-make, test and update the info.

> > 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. :-)
>
OK, thanks!

Thanks,
Tao Liu

> --
> Regards/Gruss,
>     Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette
>