efi/x86: Don't relocate the kernel unless necessary

Add alignment slack to the PE image size, so that we can realign the
decompression buffer within the space allocated for the image.

Only relocate the kernel if it has been loaded at an unsuitable address:

 - Below LOAD_PHYSICAL_ADDR, or
 - Above 64T for 64-bit and 512MiB for 32-bit

For 32-bit, the upper limit is conservative, but the exact limit can be
difficult to calculate.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200303221205.4048668-6-nivedita@alum.mit.edu
Link: https://lore.kernel.org/r/20200308080859.21568-20-ardb@kernel.org

1 files changed, 6 insertions, 10 deletions

diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
index 8cac5b6103db..8f8c8e386cea 100644
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -238,21 +238,17 @@ static void update_pecoff_text(unsigned int text_start, unsigned int file_sz,
 
 	pe_header = get_unaligned_le32(&buf[0x3c]);
 
-#ifdef CONFIG_EFI_MIXED
 	/*
-	 * In mixed mode, we will execute startup_32() at whichever offset in
-	 * memory it happened to land when the PE/COFF loader loaded the image,
-	 * which may be misaligned with respect to the kernel_alignment field
-	 * in the setup header.
+	 * The PE/COFF loader may load the image at an address which is
+	 * misaligned with respect to the kernel_alignment field in the setup
+	 * header.
 	 *
-	 * In order for startup_32 to safely execute in place at this offset,
-	 * we need to ensure that the CONFIG_PHYSICAL_ALIGN aligned allocation
-	 * it creates for the page tables does not extend beyond the declared
-	 * size of the image in the PE/COFF header. So add the required slack.
+	 * In order to avoid relocating the kernel to correct the misalignment,
+	 * add slack to allow the buffer to be aligned within the declared size
+	 * of the image.
 	 */
 	bss_sz	+= CONFIG_PHYSICAL_ALIGN;
 	init_sz	+= CONFIG_PHYSICAL_ALIGN;
-#endif
 
 	/*
 	 * Size of code: Subtract the size of the first sector (512 bytes)