linux-kernel - Re: [PATCH v2] x86/efi: Disable runtime services on kexec kernel if booted with efi=old

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Date:   Tue, 16 May 2017 18:59:29 -0700
From:   Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        Ricardo Neri <ricardo.neri@...el.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Ravi Shankar <ravi.v.shankar@...el.com>,
        Lee Chun-Yi <jlee@...e.com>
Subject: Re: [PATCH v2] x86/efi: Disable runtime services on kexec kernel if
 booted with efi=old_map

On Wed, 2017-05-17 at 09:57 +0800, Dave Young wrote:
> Hi Sai,
> On 05/16/17 at 06:14pm, Sai Praneeth Prakhya wrote:
> > From: Sai Praneeth <sai.praneeth.prakhya@...el.com>
> > 
> > Booting kexec kernel with "efi=old_map" in kernel command line hits
> > kernel panic as shown below.
> > 
> > [0.001000] BUG: unable to handle kernel paging request at ffff88007fe78070
> > [0.001000] IP: virt_efi_set_variable.part.7+0x63/0x1b0
> > [0.001000] PGD 7ea28067
> > [0.001000] PUD 7ea2b067
> > [0.001000] PMD 7ea2d067
> > [0.001000] PTE 0
> > [0.001000]
> > [0.001000] Oops: 0000 [#1] SMP
> > [0.001000] Modules linked in:
> > [0.001000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.11.0-rc2-yocto-standard+ #229
> > [0.001000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
> > [0.001000] task: ffffffff82022500 task.stack: ffffffff82000000
> > [0.001000] RIP: 0010:virt_efi_set_variable.part.7+0x63/0x1b0
> > [0.001000] RSP: 0000:ffffffff82003dc0 EFLAGS: 00010246
> > [0.001000] RAX: ffff88007fe78018 RBX: ffffffff82050300 RCX: 0000000000000007
> > [0.001000] RDX: ffffffff82003e50 RSI: ffffffff82050300 RDI: ffffffff82050300
> > [0.001000] RBP: ffffffff82003e08 R08: 0000000000000000 R09: 0000000000000000
> > [0.001000] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff82003e50
> > [0.001000] R13: 0000000000000007 R14: 0000000000000246 R15: 0000000000000000
> > [0.001000] FS:  0000000000000000(0000) GS:ffff88007fa00000(0000) knlGS:0000000000000000
> > [0.001000] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [0.001000] CR2: ffff88007fe78070 CR3: 000000007da1d000 CR4: 00000000000006b0
> > [0.001000] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [0.001000] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > [0.001000] Call Trace:
> > [0.001000]  virt_efi_set_variable+0x5d/0x70
> > [0.001000]  efi_delete_dummy_variable+0x7a/0x80
> > [0.001000]  efi_enter_virtual_mode+0x3f6/0x4a7
> > [0.001000]  start_kernel+0x375/0x400
> > [0.001000]  x86_64_start_reservations+0x2a/0x2c
> > [0.001000]  x86_64_start_kernel+0x168/0x176
> > [0.001000]  start_cpu+0x14/0x14
> > [0.001000] Code: 04 b0 84 ff 80 3d c5 56 b3 00 00 4c 8b 44 24 08 75
> > 6b 9c 41 5e 48 8b 05 9c 78 99 00 4d 89 c1 48 89 de 4d 89 f8 44 89 e9 4c
> > 89 e2 <48> 8b 40 58 48 8b 78 58 e8 b0 2d 88 ff 48 c7 c6 b6 1d f4 81 4c
> > [0.001000] RIP: virt_efi_set_variable.part.7+0x63/0x1b0 RSP: ffffffff82003dc0
> > [0.001000] CR2: ffff88007fe78070
> > [0.001000] ---[ end trace 0000000000000000 ]---
> > [0.001000] Kernel panic - not syncing: Attempted to kill the idle task!
> > [0.001000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task!
> > 
> > [efi=old_map was never intended to work with kexec. The problem with
> > using efi=old_map is that the virtual addresses are assigned from the
> > memory region used by other kernel mappings; vmalloc() space.
> > Potentially there could be collisions when booting kexec if something
> > else is mapped at the virtual address we allocated for runtime service
> > regions in the initial boot] - Matt Fleming
> > 
> > Since kexec was never intended to work with efi=old_map, disable
> > runtime services in kexec if booted with efi=old_map, so that we don't
> > panic.
> > 
> > Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Ricardo Neri <ricardo.neri@...el.com>
> > Cc: Matt Fleming <matt@...eblueprint.co.uk>
> > Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> > Cc: Ravi Shankar <ravi.v.shankar@...el.com>
> > Cc: Lee Chun-Yi <jlee@...e.com>
> > Cc: Dave Young <dyoung@...hat.com>
> > 
> > Changes since v1:
> > Don't fix the panic, because this was never intended to work.
> > ---
> >  arch/x86/platform/efi/efi.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> > index 87835c97611f..627b7b86f369 100644
> > --- a/arch/x86/platform/efi/efi.c
> > +++ b/arch/x86/platform/efi/efi.c
> > @@ -827,9 +827,11 @@ static void __init kexec_enter_virtual_mode(void)
> >  
> >  	/*
> >  	 * We don't do virtual mode, since we don't do runtime services, on
> > -	 * non-native EFI
> > +	 * non-native EFI. With efi=old_map, we don't do runtime services in
> > +	 * kexec kernel because in the initial boot something else might
> > +	 * have been mapped at these virtual addresses.
> >  	 */
> > -	if (!efi_is_native()) {
> > +	if (!efi_is_native() || efi_enabled(EFI_OLD_MEMMAP)) {
> >  		efi_memmap_unmap();
> >  		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
> >  		return;
> > -- 
> > 2.1.4
> > 
> 
> Suppose it has passed the test on your hardware:
> Acked-by: Dave Young <dyoung@...hat.com>
> 

Thanks Dave! Haha... yes.
I tested on qemu with OVMF

> Thanks
> Dave

Regards,
Sai