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Date: Tue, 3 Mar 2020 17:12:00 -0500
From: Arvind Sankar <nivedita@...m.mit.edu>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: linux-efi@...r.kernel.org, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/5] Minimize the need to move the kernel in the EFI stub
This series adds the ability to use the entire PE image space for
decompression, provides the preferred address to the PE loader via the
header, and finally restricts efi_relocate_kernel to cases where we
really need it rather than whenever we were loaded at something other
than preferred address.
Based on tip:efi/core + the cleanup series [1]
[1] https://lore.kernel.org/linux-efi/20200301230436.2246909-1-nivedita@alum.mit.edu/
Changes from v1
- clarify a few comments
- cleanups to code formatting
Arvind Sankar (5):
x86/boot/compressed/32: Save the output address instead of
recalculating it
efi/x86: Decompress at start of PE image load address
efi/x86: Add kernel preferred address to PE header
efi/x86: Remove extra headroom for setup block
efi/x86: Don't relocate the kernel unless necessary
arch/x86/boot/compressed/head_32.S | 42 +++++++++++++++-------
arch/x86/boot/compressed/head_64.S | 42 ++++++++++++++++++++--
arch/x86/boot/header.S | 6 ++--
arch/x86/boot/tools/build.c | 44 ++++++++++++++++-------
drivers/firmware/efi/libstub/x86-stub.c | 48 ++++++++++++++++++++++---
5 files changed, 147 insertions(+), 35 deletions(-)
Range-diff against v1:
1: 0cdb6bf27a24 ! 1: 2ecbf60b9ecd x86/boot/compressed/32: Save the output address instead of recalculating it
@@ Metadata
## Commit message ##
x86/boot/compressed/32: Save the output address instead of recalculating it
- In preparation for being able to decompress starting at a different
- address than startup_32, save the calculated output address instead of
- recalculating it later.
+ In preparation for being able to decompress into a buffer starting at a
+ different address than startup_32, save the calculated output address
+ instead of recalculating it later.
We now keep track of three addresses:
%edx: startup_32 as we were loaded by bootloader
2: d4df840752ac ! 2: e2bdbe6cb692 efi/x86: Decompress at start of PE image load address
@@ arch/x86/boot/compressed/head_64.S: SYM_FUNC_START(efi32_pe_entry)
movl -4(%ebp), %esi // loaded_image
movl LI32_image_base(%esi), %esi // loaded_image->image_base
movl %ebx, %ebp // startup_32 for efi32_pe_stub_entry
++ /*
++ * We need to set the image_offset variable here since startup_32 will
++ * use it before we get to the 64-bit efi_pe_entry in C code.
++ */
+ subl %esi, %ebx
+ movl %ebx, image_offset(%ebp) // save image_offset
jmp efi32_pe_stub_entry
@@ drivers/firmware/efi/libstub/x86-stub.c: unsigned long efi_main(efi_handle_t han
efi_printk("efi_relocate_kernel() failed!\n");
goto fail;
}
++ /*
++ * Now that we've copied the kernel elsewhere, we no longer
++ * have a setup block before startup_32, so reset image_offset
++ * to zero in case it was set earlier.
++ */
+ image_offset = 0;
}
3: 4bae68f25b90 ! 3: ea840f78f138 efi/x86: Add kernel preferred address to PE header
@@ arch/x86/boot/header.S: optional_header:
extra_header_fields:
+ # PE specification requires ImageBase to be 64k-aligned
-+ .set ImageBase, (LOAD_PHYSICAL_ADDR+0xffff) & ~0xffff
++ .set image_base, (LOAD_PHYSICAL_ADDR + 0xffff) & ~0xffff
#ifdef CONFIG_X86_32
- .long 0 # ImageBase
-+ .long ImageBase # ImageBase
++ .long image_base # ImageBase
#else
- .quad 0 # ImageBase
-+ .quad ImageBase # ImageBase
++ .quad image_base # ImageBase
#endif
.long 0x20 # SectionAlignment
.long 0x20 # FileAlignment
4: 2330a25c6b0f ! 4: c25a9b507d6d efi/x86: Remove extra headroom for setup block
@@ Commit message
account for setup block") added headroom to the PE image to account for
the setup block, which wasn't used for the decompression buffer.
- Now that we decompress from the start of the image, this is no longer
- required.
+ Now that the decompression buffer is located at the start of the image,
+ and includes the setup block, this is no longer required.
Add a check to make sure that the head section of the compressed kernel
won't overwrite itself while relocating. This is only for
5: 2081f91cbe75 ! 5: d3dc3af1c7b8 efi/x86: Don't relocate the kernel unless necessary
@@ arch/x86/boot/tools/build.c: static void update_pecoff_text(unsigned int text_st
* Size of code: Subtract the size of the first sector (512 bytes)
## drivers/firmware/efi/libstub/x86-stub.c ##
+@@
+
+ #include "efistub.h"
+
++/* Maximum physical address for 64-bit kernel with 4-level paging */
++#define MAXMEM_X86_64_4LEVEL (1ull << 46)
++
+ static efi_system_table_t *sys_table;
+ extern const bool efi_is64;
+ extern u32 image_offset;
@@ drivers/firmware/efi/libstub/x86-stub.c: unsigned long efi_main(efi_handle_t handle,
struct boot_params *boot_params)
{
@@ drivers/firmware/efi/libstub/x86-stub.c: unsigned long efi_main(efi_handle_t han
- * address, relocate it.
+ * If the kernel isn't already loaded at a suitable address,
+ * relocate it.
++ *
+ * It must be loaded above LOAD_PHYSICAL_ADDR.
-+ * The maximum address for 64-bit is 1 << 46 for 4-level paging.
++ *
++ * The maximum address for 64-bit is 1 << 46 for 4-level paging. This
++ * is defined as the macro MAXMEM, but unfortunately that is not a
++ * compile-time constant if 5-level paging is configured, so we instead
++ * define our own macro for use here.
++ *
+ * For 32-bit, the maximum address is complicated to figure out, for
+ * now use KERNEL_IMAGE_SIZE, which will be 512MiB, the same as what
+ * KASLR uses.
++ *
+ * Also relocate it if image_offset is zero, i.e. we weren't loaded by
+ * LoadImage, but we are not aligned correctly.
*/
- if (bzimage_addr - image_offset != hdr->pref_address) {
++
+ buffer_start = ALIGN(bzimage_addr - image_offset,
+ hdr->kernel_alignment);
+ buffer_end = buffer_start + hdr->init_size;
+
-+ if (buffer_start < LOAD_PHYSICAL_ADDR
-+ || IS_ENABLED(CONFIG_X86_32) && buffer_end > KERNEL_IMAGE_SIZE
-+ || IS_ENABLED(CONFIG_X86_64) && buffer_end > 1ull << 46
-+ || image_offset == 0 && !IS_ALIGNED(bzimage_addr,
-+ hdr->kernel_alignment)) {
++ if ((buffer_start < LOAD_PHYSICAL_ADDR) ||
++ (IS_ENABLED(CONFIG_X86_32) && buffer_end > KERNEL_IMAGE_SIZE) ||
++ (IS_ENABLED(CONFIG_X86_64) && buffer_end > MAXMEM_X86_64_4LEVEL) ||
++ (image_offset == 0 && !IS_ALIGNED(bzimage_addr,
++ hdr->kernel_alignment))) {
status = efi_relocate_kernel(&bzimage_addr,
hdr->init_size, hdr->init_size,
hdr->pref_address,
--
2.24.1
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