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

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Date:   Tue, 16 May 2017 18:14:23 -0700
From:   Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
To:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Sai Praneeth <sai.praneeth.prakhya@...el.com>,
        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>, Dave Young <dyoung@...hat.com>
Subject: [PATCH v2] x86/efi: Disable runtime services on kexec kernel if booted with efi=old_map

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