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From:   Kairui Song <kasong@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Matthew Garrett <matthewgarrett@google.com>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Baoquan He <bhe@redhat.com>, Dave Young <dyoung@redhat.com>,
        x86@kernel.org, linux-efi@vger.kernel.org,
        Kairui Song <kasong@redhat.com>
Subject: [PATCH v4] x86, efi: never relocate kernel below lowest acceptable address
Date:   Thu, 17 Oct 2019 17:30:20 +0800
Message-Id: <20191017093020.28658-1-kasong@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Currently, kernel fails to boot on some HyperV VMs when using EFI.
And it's a potential issue on all platforms.

It's caused by broken kernel relocation on EFI systems, when below three
conditions are met:

1. Kernel image is not loaded to the default address (LOAD_PHYSICAL_ADDR)
   by the loader.
2. There isn't enough room to contain the kernel, starting from the
   default load address (eg. something else occupied part the region).
3. In the memmap provided by EFI firmware, there is a memory region
   starts below LOAD_PHYSICAL_ADDR, and suitable for containing the
   kernel.

EFI stub will perform a kernel relocation when condition 1 is met. But
due to condition 2, EFI stub can't relocate kernel to the preferred
address, so it fallback to ask EFI firmware to alloc lowest usable memory
region, got the low region mentioned in condition 3, and relocated
kernel there.

It's incorrect to relocate the kernel below LOAD_PHYSICAL_ADDR. This
is the lowest acceptable kernel relocation address.

The first thing goes wrong is in arch/x86/boot/compressed/head_64.S.
Kernel decompression will force use LOAD_PHYSICAL_ADDR as the output
address if kernel is located below it. Then the relocation before
decompression, which move kernel to the end of the decompression buffer,
will overwrite other memory region, as there is no enough memory there.

To fix it, just don't let EFI stub relocate the kernel to any address
lower than lowest acceptable address.

Signed-off-by: Kairui Song <kasong@redhat.com>
Acked-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

---
Update from V3:
 - Update commit message.

Update from V2:
 - Update part of the commit message.

Update from V1:
 - Redo the commit message.

 arch/x86/boot/compressed/eboot.c               |  8 +++++---
 drivers/firmware/efi/libstub/arm32-stub.c      |  2 +-
 drivers/firmware/efi/libstub/arm64-stub.c      |  2 +-
 drivers/firmware/efi/libstub/efi-stub-helper.c | 12 ++++++++----
 include/linux/efi.h                            |  5 +++--
 5 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index d6662fdef300..e89e84b66527 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -13,6 +13,7 @@
 #include <asm/e820/types.h>
 #include <asm/setup.h>
 #include <asm/desc.h>
+#include <asm/boot.h>
 
 #include "../string.h"
 #include "eboot.h"
@@ -413,7 +414,7 @@ struct boot_params *make_boot_params(struct efi_config *c)
 	}
 
 	status = efi_low_alloc(sys_table, 0x4000, 1,
-			       (unsigned long *)&boot_params);
+			       (unsigned long *)&boot_params, 0);
 	if (status != EFI_SUCCESS) {
 		efi_printk(sys_table, "Failed to allocate lowmem for boot params\n");
 		return NULL;
@@ -798,7 +799,7 @@ efi_main(struct efi_config *c, struct boot_params *boot_params)
 
 	gdt->size = 0x800;
 	status = efi_low_alloc(sys_table, gdt->size, 8,
-			   (unsigned long *)&gdt->address);
+			       (unsigned long *)&gdt->address, 0);
 	if (status != EFI_SUCCESS) {
 		efi_printk(sys_table, "Failed to allocate memory for 'gdt'\n");
 		goto fail;
@@ -813,7 +814,8 @@ efi_main(struct efi_config *c, struct boot_params *boot_params)
 		status = efi_relocate_kernel(sys_table, &bzimage_addr,
 					     hdr->init_size, hdr->init_size,
 					     hdr->pref_address,
-					     hdr->kernel_alignment);
+					     hdr->kernel_alignment,
+					     LOAD_PHYSICAL_ADDR);
 		if (status != EFI_SUCCESS) {
 			efi_printk(sys_table, "efi_relocate_kernel() failed!\n");
 			goto fail;
diff --git a/drivers/firmware/efi/libstub/arm32-stub.c b/drivers/firmware/efi/libstub/arm32-stub.c
index e8f7aefb6813..bf6f954d6afe 100644
--- a/drivers/firmware/efi/libstub/arm32-stub.c
+++ b/drivers/firmware/efi/libstub/arm32-stub.c
@@ -220,7 +220,7 @@ efi_status_t handle_kernel_image(efi_system_table_t *sys_table,
 	*image_size = image->image_size;
 	status = efi_relocate_kernel(sys_table, image_addr, *image_size,
 				     *image_size,
-				     dram_base + MAX_UNCOMP_KERNEL_SIZE, 0);
+				     dram_base + MAX_UNCOMP_KERNEL_SIZE, 0, 0);
 	if (status != EFI_SUCCESS) {
 		pr_efi_err(sys_table, "Failed to relocate kernel.\n");
 		efi_free(sys_table, *reserve_size, *reserve_addr);
diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
index 1550d244e996..3d2e517e10f4 100644
--- a/drivers/firmware/efi/libstub/arm64-stub.c
+++ b/drivers/firmware/efi/libstub/arm64-stub.c
@@ -140,7 +140,7 @@ efi_status_t handle_kernel_image(efi_system_table_t *sys_table_arg,
 	if (status != EFI_SUCCESS) {
 		*reserve_size = kernel_memsize + TEXT_OFFSET;
 		status = efi_low_alloc(sys_table_arg, *reserve_size,
-				       MIN_KIMG_ALIGN, reserve_addr);
+				       MIN_KIMG_ALIGN, reserve_addr, 0);
 
 		if (status != EFI_SUCCESS) {
 			pr_efi_err(sys_table_arg, "Failed to relocate kernel\n");
diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index 3caae7f2cf56..00b00a2562aa 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -260,11 +260,11 @@ efi_status_t efi_high_alloc(efi_system_table_t *sys_table_arg,
 }
 
 /*
- * Allocate at the lowest possible address.
+ * Allocate at the lowest possible address that is not below 'min'.
  */
 efi_status_t efi_low_alloc(efi_system_table_t *sys_table_arg,
 			   unsigned long size, unsigned long align,
-			   unsigned long *addr)
+			   unsigned long *addr, unsigned long min)
 {
 	unsigned long map_size, desc_size, buff_size;
 	efi_memory_desc_t *map;
@@ -311,6 +311,9 @@ efi_status_t efi_low_alloc(efi_system_table_t *sys_table_arg,
 		start = desc->phys_addr;
 		end = start + desc->num_pages * EFI_PAGE_SIZE;
 
+		if (start < min)
+			start = min;
+
 		/*
 		 * Don't allocate at 0x0. It will confuse code that
 		 * checks pointers against NULL. Skip the first 8
@@ -698,7 +701,8 @@ efi_status_t efi_relocate_kernel(efi_system_table_t *sys_table_arg,
 				 unsigned long image_size,
 				 unsigned long alloc_size,
 				 unsigned long preferred_addr,
-				 unsigned long alignment)
+				 unsigned long alignment,
+				 unsigned long min_addr)
 {
 	unsigned long cur_image_addr;
 	unsigned long new_addr = 0;
@@ -732,7 +736,7 @@ efi_status_t efi_relocate_kernel(efi_system_table_t *sys_table_arg,
 	 */
 	if (status != EFI_SUCCESS) {
 		status = efi_low_alloc(sys_table_arg, alloc_size, alignment,
-				       &new_addr);
+				       &new_addr, min_addr);
 	}
 	if (status != EFI_SUCCESS) {
 		pr_efi_err(sys_table_arg, "Failed to allocate usable memory for kernel.\n");
diff --git a/include/linux/efi.h b/include/linux/efi.h
index bd3837022307..a5144cc44e54 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1581,7 +1581,7 @@ efi_status_t efi_get_memory_map(efi_system_table_t *sys_table_arg,
 
 efi_status_t efi_low_alloc(efi_system_table_t *sys_table_arg,
 			   unsigned long size, unsigned long align,
-			   unsigned long *addr);
+			   unsigned long *addr, unsigned long min);
 
 efi_status_t efi_high_alloc(efi_system_table_t *sys_table_arg,
 			    unsigned long size, unsigned long align,
@@ -1592,7 +1592,8 @@ efi_status_t efi_relocate_kernel(efi_system_table_t *sys_table_arg,
 				 unsigned long image_size,
 				 unsigned long alloc_size,
 				 unsigned long preferred_addr,
-				 unsigned long alignment);
+				 unsigned long alignment,
+				 unsigned long min_addr);
 
 efi_status_t handle_cmdline_files(efi_system_table_t *sys_table_arg,
 				  efi_loaded_image_t *image,
-- 
2.21.0