linux-kernel - [PATCH 3/5] x86/efi: Disable runtime services on kexec kernel if booted with efi=old

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Message-Id: <20170526113652.21339-4-matt@codeblueprint.co.uk>
Date:   Fri, 26 May 2017 12:36:49 +0100
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     Sai Praneeth <sai.praneeth.prakhya@...el.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Borislav Petkov <bp@...en8.de>, Dave Young <dyoung@...hat.com>,
        Lee Chun-Yi <jlee@...e.com>,
        Ravi Shankar <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>
Subject: [PATCH 3/5] 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.

 BUG: unable to handle kernel paging request at ffff88007fe78070
 IP: virt_efi_set_variable.part.7+0x63/0x1b0
 PGD 7ea28067
 PUD 7ea2b067
 PMD 7ea2d067
 PTE 0
 [...]
 Call Trace:
  virt_efi_set_variable+0x5d/0x70
  efi_delete_dummy_variable+0x7a/0x80
  efi_enter_virtual_mode+0x3f6/0x4a7
  start_kernel+0x375/0x400
  x86_64_start_reservations+0x2a/0x2c
  x86_64_start_kernel+0x168/0x176
  start_cpu+0x14/0x14

[ 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: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Ravi Shankar <ravi.v.shankar@...el.com>
Tested-by: Lee Chun-Yi <jlee@...e.com>
Acked-by: Dave Young <dyoung@...hat.com>
Signed-off-by: Matt Fleming <matt@...eblueprint.co.uk>
---
 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 7e76a4d8304b..43b96f5f78ba 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -828,9 +828,11 @@ 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;
-- 
2.12.2