[PATCH] kexec: don't act as EFI chainloader if noefi.

Chris Koch chrisko at google.com
Wed Oct 17 16:41:39 PDT 2018


From: Christopher Koch <chrisko at google.com>

An EFI-booted Linux kernel will commit a virtual memory map in
efi_enter_virtual_mode, which is only done if
efi_enabled(EFI_RUNTIME_SERVICES). This can be disabled by adding noefi
to the command line.

kexec's setup_efi_state will then pass a memmap_size of 0 to the next
kernel.

A Linux kernel cannot handle a memmap_size of 0 given by its bootloader:
efi_memblock_x86_reserve_range divides by the memmap_size and hits a
divide by 0 error.

When the 1st kernel is booted with noefi, it should not even attempt to
pass EFI information to any kexec'd kernel.

Signed-off-by: Christopher Koch <chrisko at google.com>
---
 arch/x86/kernel/kexec-bzimage64.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
index 278cd07228dd..8ab4ffb901ce 100644
--- a/arch/x86/kernel/kexec-bzimage64.c
+++ b/arch/x86/kernel/kexec-bzimage64.c
@@ -179,6 +179,14 @@ setup_efi_state(struct boot_params *params, unsigned long params_load_addr,
 	if (efi_enabled(EFI_OLD_MEMMAP))
 		return 0;
 
+	/*
+	 * If we booted with noefi on the command line, we never committed a
+	 * virtual memory map. It makes no sense to act as an EFI chainloader in
+	 * that case.
+	 */
+	if (!efi_enabled(EFI_RUNTIME_SERVICES))
+		return 0;
+
 	ei->efi_loader_signature = current_ei->efi_loader_signature;
 	ei->efi_systab = current_ei->efi_systab;
 	ei->efi_systab_hi = current_ei->efi_systab_hi;
-- 
2.19.1.331.ge82ca0e54c-goog




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