Fix for "Section 0 has negative size" error when loading fbaa64.efi

The current code is incorrectly failing to load the fbaa64.efi image found
in Arm servers even though the UEFI shell code is able to properly load
and execute the same image.

The problem is due to the presence of a section header that has zero size
and address and marked "discardable" in the fbaa64.efi image.

Although there is already a check further down in the code to look for
the discardable bit and skip further verification checks if set, we never
get to that point due to the "end < base" check at the start of the loop.

Here is a dump of the fbaa64.efi image as compiled on an Arm machine
from the latest code in this repo:

% # First I used hexedit to change header byte from 'AA' to '86'
% # so that objdump was able to correctly parse the file:
% objdump -x -m aarch64 fbaa64.efi

fbaa64.efi:     file format pei-x86-64
fbaa64.efi
architecture: i386:x86-64, flags 0x00000103:
HAS_RELOC, EXEC_P, D_PAGED
start address 0x0000000000000148

Characteristics 0x20e
        executable
        line numbers stripped
        symbols stripped
        debugging information removed

Time/Date               Wed Dec 31 16:00:00 1969
Magic                   020b    (PE32+)
MajorLinkerVersion      2
MinorLinkerVersion      20
SizeOfCode              000b15d0
SizeOfInitializedData   00000000
SizeOfUninitializedData 00000000
AddressOfEntryPoint     0000000000000148
BaseOfCode              0000000000000148
ImageBase               0000000000000000
SectionAlignment        0000000000000020
FileAlignment           0000000000000008
MajorOSystemVersion     0
MinorOSystemVersion     0
MajorImageVersion       0
MinorImageVersion       0
MajorSubsystemVersion   0
MinorSubsystemVersion   0
Win32Version            00000000
SizeOfImage             000b1718
SizeOfHeaders           00000148
CheckSum                00000000
Subsystem               0000000a        (EFI application)
DllCharacteristics      00000000
SizeOfStackReserve      0000000000000000
SizeOfStackCommit       0000000000000000
SizeOfHeapReserve       0000000000000000
SizeOfHeapCommit        0000000000000000
LoaderFlags             00000000
NumberOfRvaAndSizes     00000006

The Data Directory
Entry 0 0000000000000000 00000000 Export Directory [.edata (or where ever we found it)]
Entry 1 0000000000000000 00000000 Import Directory [parts of .idata]
Entry 2 0000000000000000 00000000 Resource Directory [.rsrc]
Entry 3 0000000000000000 00000000 Exception Directory [.pdata]
Entry 4 0000000000000000 00000000 Security Directory
Entry 5 0000000000000000 00000000 Base Relocation Directory [.reloc]
Entry 6 0000000000000000 00000000 Debug Directory
Entry 7 0000000000000000 00000000 Description Directory
Entry 8 0000000000000000 00000000 Special Directory
Entry 9 0000000000000000 00000000 Thread Storage Directory [.tls]
Entry a 0000000000000000 00000000 Load Configuration Directory
Entry b 0000000000000000 00000000 Bound Import Directory
Entry c 0000000000000000 00000000 Import Address Table Directory
Entry d 0000000000000000 00000000 Delay Import Directory
Entry e 0000000000000000 00000000 CLR Runtime Header
Entry f 0000000000000000 00000000 Reserved

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  0 .reloc        00000000  0000000000000000  0000000000000000  00000000  2**0
                  ALLOC, LOAD, READONLY, DATA
  1 .text         000b15d0  0000000000000148  0000000000000148  00000148  2**4
                  CONTENTS, ALLOC, LOAD, CODE
SYMBOL TABLE:
no symbols

Signed-off-by: Maran Wilson <maran.wilson@oracle.com>
Reviewed-by: Aaron Young <aaron.young@oracle.com>
Reviewed-by: Jack Schwartz <jack.schwartz@oracle.com>
Upstream-commit-id: 6df7a8f5609

1 files changed, 5 insertions, 0 deletions

diff --git a/shim.c b/shim.c
index ae03da7e..d980cada 100644
--- a/shim.c
+++ b/shim.c
@@ -1347,6 +1347,11 @@ static EFI_STATUS handle_image (void *data, unsigned int datasize,
 	 */
 	Section = context.FirstSection;
 	for (i = 0; i < context.NumberOfSections; i++, Section++) {
+		/* Don't try to copy discardable sections with zero size */
+		if ((Section->Characteristics & EFI_IMAGE_SCN_MEM_DISCARDABLE) &&
+		    !Section->Misc.VirtualSize)
+			continue;
+
 		base = ImageAddress (buffer, context.ImageSize,
 				     Section->VirtualAddress);
 		end = ImageAddress (buffer, context.ImageSize,