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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Laszlo Ersek <lersek@redhat.com>
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Date: Wed, 23 Nov 2016 06:27:09 +0100
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Subject: [PATCH] efi/chainloader: truncate overlong relocation section
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The UEFI Windows 7 boot loader ("EFI/Microsoft/Boot/bootmgfw.efi", SHA1
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31b410e029bba87d2068c65a80b88882f9f8ea25) has inconsistent headers.
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Compare:
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> The Data Directory
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> ...
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> Entry 5 00000000000d9000 00000574 Base Relocation Directory [.reloc]
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Versus:
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> Sections:
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> Idx Name Size VMA LMA File off ...
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> ...
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> 10 .reloc 00000e22 00000000100d9000 00000000100d9000 000a1800 ...
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That is, the size reported by the RelocDir entry (0x574) is smaller than
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the virtual size of the .reloc section (0xe22).
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Quoting the grub2 debug log for the same:
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> chainloader.c:595: reloc_dir: 0xd9000 reloc_size: 0x00000574
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> chainloader.c:603: reloc_base: 0x7d208000 reloc_base_end: 0x7d208573
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> ...
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> chainloader.c:620: Section 10 ".reloc" at 0x7d208000..0x7d208e21
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> chainloader.c:661: section is not reloc section?
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> chainloader.c:663: rds: 0x00001000, vs: 00000e22
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> chainloader.c:664: base: 0x7d208000 end: 0x7d208e21
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> chainloader.c:666: reloc_base: 0x7d208000 reloc_base_end: 0x7d208573
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> chainloader.c:671: Section characteristics are 42000040
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> chainloader.c:673: Section virtual size: 00000e22
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> chainloader.c:675: Section raw_data size: 00001000
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> chainloader.c:678: Discarding section
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After hexdumping "bootmgfw.efi" and manually walking its relocation blocks
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(yes, really), I determined that the (smaller) RelocDir value is correct.
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The remaining area that extends up to the .reloc section size (== 0xe22 -
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0x574 == 0x8ae bytes) exists as zero padding in the file.
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This zero padding shouldn't be passed to relocate_coff() for parsing. In
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order to cope with it, split the handling of .reloc sections into the
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following branches:
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- original case (equal size): original behavior (--> relocation
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attempted),
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- overlong .reloc section (longer than reported by RelocDir): truncate the
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section to the RelocDir size for the purposes of relocate_coff(), and
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attempt relocation,
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- .reloc section is too short, or other checks fail: original behavior
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(--> relocation not attempted).
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1347291
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Signed-off-by: Laszlo Ersek <lersek@redhat.com>
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---
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grub-core/loader/efi/chainloader.c | 26 +++++++++++++++++++++-----
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1 file changed, 21 insertions(+), 5 deletions(-)
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diff --git a/grub-core/loader/efi/chainloader.c b/grub-core/loader/efi/chainloader.c
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index ed8c364789a..db1ffeefc93 100644
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--- a/grub-core/loader/efi/chainloader.c
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+++ b/grub-core/loader/efi/chainloader.c
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@@ -596,7 +596,7 @@ handle_image (void *data, grub_efi_uint32_t datasize)
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grub_dprintf ("chain", "reloc_base: %p reloc_base_end: %p\n",
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reloc_base, reloc_base_end);
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- struct grub_pe32_section_table *reloc_section = NULL;
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+ struct grub_pe32_section_table *reloc_section = NULL, fake_reloc_section;
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section = context.first_section;
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for (i = 0; i < context.number_of_sections; i++, section++)
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@@ -645,12 +645,28 @@ handle_image (void *data, grub_efi_uint32_t datasize)
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* made sense, and the VA and size match RelocDir's
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* versions, then we believe in this section table. */
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if (section->raw_data_size && section->virtual_size &&
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- base && end && reloc_base == base && reloc_base_end == end)
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+ base && end && reloc_base == base)
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{
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- grub_dprintf ("chain", " section is relocation section\n");
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- reloc_section = section;
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+ if (reloc_base_end == end)
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+ {
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+ grub_dprintf ("chain", " section is relocation section\n");
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+ reloc_section = section;
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+ }
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+ else if (reloc_base_end && reloc_base_end < end)
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+ {
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+ /* Bogus virtual size in the reloc section -- RelocDir
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+ * reported a smaller Base Relocation Directory. Decrease
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+ * the section's virtual size so that it equal RelocDir's
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+ * idea, but only for the purposes of relocate_coff(). */
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+ grub_dprintf ("chain",
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+ " section is (overlong) relocation section\n");
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+ grub_memcpy (&fake_reloc_section, section, sizeof *section);
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+ fake_reloc_section.virtual_size -= (end - reloc_base_end);
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+ reloc_section = &fake_reloc_section;
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+ }
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}
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- else
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+
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+ if (!reloc_section)
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{
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grub_dprintf ("chain", " section is not reloc section?\n");
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grub_dprintf ("chain", " rds: 0x%08x, vs: %08x\n",
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