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Date:   Wed, 08 Aug 2018 16:03:45 +0200
From:   Mike Galbraith <efault@....de>
To:     Dave Young <dyoung@...hat.com>
Cc:     Baoquan He <bhe@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        lkml <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86, kdump: Fix efi=noruntime NULL pointer dereference

When booting with efi=noruntime, we call efi_runtime_map_copy() while
loading the kdump kernel, and trip over a NULL efi.memmap.map.  Avoid
that and a useless allocation when the only mapping we can use (1:1)
is not available.

Signed-off-by: Mike Galbraith <efault@....de>
---
 arch/x86/kernel/kexec-bzimage64.c |   22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

--- a/arch/x86/kernel/kexec-bzimage64.c
+++ b/arch/x86/kernel/kexec-bzimage64.c
@@ -122,9 +122,6 @@ static int setup_efi_info_memmap(struct
 	unsigned long efi_map_phys_addr = params_load_addr + efi_map_offset;
 	struct efi_info *ei = &params->efi_info;
 
-	if (!efi_map_sz)
-		return 0;
-
 	efi_runtime_map_copy(efi_map, efi_map_sz);
 
 	ei->efi_memmap = efi_map_phys_addr & 0xffffffff;
@@ -176,7 +173,7 @@ setup_efi_state(struct boot_params *para
 	 * acpi_rsdp=<addr> on kernel command line to make second kernel boot
 	 * without efi.
 	 */
-	if (efi_enabled(EFI_OLD_MEMMAP))
+	if (efi_enabled(EFI_OLD_MEMMAP) || !efi_enabled(EFI_MEMMAP))
 		return 0;
 
 	ei->efi_loader_signature = current_ei->efi_loader_signature;
@@ -338,7 +335,7 @@ static void *bzImage64_load(struct kimag
 	struct kexec_entry64_regs regs64;
 	void *stack;
 	unsigned int setup_hdr_offset = offsetof(struct boot_params, hdr);
-	unsigned int efi_map_offset, efi_map_sz, efi_setup_data_offset;
+	unsigned int efi_map_offset = 0, efi_map_sz = 0, efi_setup_data_offset = 0;
 	struct kexec_buf kbuf = { .image = image, .buf_max = ULONG_MAX,
 				  .top_down = true };
 	struct kexec_buf pbuf = { .image = image, .buf_min = MIN_PURGATORY_ADDR,
@@ -397,19 +394,22 @@ static void *bzImage64_load(struct kimag
 	 * have to create separate segment for each. Keeps things
 	 * little bit simple
 	 */
-	efi_map_sz = efi_get_runtime_map_size();
 	params_cmdline_sz = sizeof(struct boot_params) + cmdline_len +
 				MAX_ELFCOREHDR_STR_LEN;
 	params_cmdline_sz = ALIGN(params_cmdline_sz, 16);
-	kbuf.bufsz = params_cmdline_sz + ALIGN(efi_map_sz, 16) +
-				sizeof(struct setup_data) +
-				sizeof(struct efi_setup_data);
+	kbuf.bufsz = params_cmdline_sz + sizeof(struct setup_data);
+
+	/* Now add space for the efi stuff if we have a useable 1:1 mapping. */
+	if (!efi_enabled(EFI_OLD_MEMMAP) && efi_enabled(EFI_MEMMAP)) {
+		efi_map_sz = efi_get_runtime_map_size();
+		kbuf.bufsz += ALIGN(efi_map_sz, 16) + sizeof(struct efi_setup_data);
+		efi_map_offset = params_cmdline_sz;
+		efi_setup_data_offset = efi_map_offset + ALIGN(efi_map_sz, 16);
+	}
 
 	params = kzalloc(kbuf.bufsz, GFP_KERNEL);
 	if (!params)
 		return ERR_PTR(-ENOMEM);
-	efi_map_offset = params_cmdline_sz;
-	efi_setup_data_offset = efi_map_offset + ALIGN(efi_map_sz, 16);
 
 	/* Copy setup header onto bootparams. Documentation/x86/boot.txt */
 	setup_header_size = 0x0202 + kernel[0x0201] - setup_hdr_offset;

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