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

[Ard Biesheuvel]

On Mon, 17 Jul 2023 at 15:53, Tao Liu <ltao@xxxxxxxxxx> wrote:
>
> Hi Borislav,
>
> On Thu, Jul 13, 2023 at 6:05 PM Borislav Petkov <bp@xxxxxxxxx> wrote:
> >
> > On Thu, Jun 01, 2023 at 03:20:44PM +0800, Tao Liu wrote:
> > >  arch/x86/kernel/machine_kexec_64.c | 35 ++++++++++++++++++++++++++----
> > >  1 file changed, 31 insertions(+), 4 deletions(-)
> >
> > Ok, pls try this totally untested thing.
> >
> > Thx.
> >
> > ---
> > diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> > index 09dc8c187b3c..fefe27b2af85 100644
> > --- a/arch/x86/boot/compressed/sev.c
> > +++ b/arch/x86/boot/compressed/sev.c
> > @@ -404,13 +404,20 @@ void sev_enable(struct boot_params *bp)
> >         if (bp)
> >                 bp->cc_blob_address = 0;
> >
> > +       /* Check for the SME/SEV support leaf */
> > +       eax = 0x80000000;
> > +       ecx = 0;
> > +       native_cpuid(&eax, &ebx, &ecx, &edx);
> > +       if (eax < 0x8000001f)
> > +               return;
> > +
> >         /*
> >          * Setup/preliminary detection of SNP. This will be sanity-checked
> >          * against CPUID/MSR values later.
> >          */
> >         snp = snp_init(bp);
> >
> > -       /* Check for the SME/SEV support leaf */
> > +       /* Recheck the SME/SEV support leaf */
> >         eax = 0x80000000;
> >         ecx = 0;
> >         native_cpuid(&eax, &ebx, &ecx, &edx);
> >
> Thanks a lot for the patch above! Sorry for the late response. I have
> compiled and tested it locally against 6.5.0-rc1, though it can pass
> the early stage of kexec kernel bootup,

OK, so that proves that the cc_blob table access is the culprit here.
That still means that kexec on SEV is likely to explode in the exact
same way should anyone attempt that.


> however the kernel will panic
> occasionally later. The test machine is the one with Intel Atom
> x6425RE cpu which encountered the page fault issue of missing efi
> config table.
>

Agree with Boris that this seems entirely unrelated.

> ...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...


Why are you snipping the hardware name?