[PATCH] efi: Ignore unrealistically large option roms

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setup_efi_pci() tries to save a copy of each PCI option ROM as this may
be necessary for the device driver for the PCI device to have access too.

On some systems the efi_pci_io_protocol_64's romimage and romsize fields
contain invalid data, which looks a bit like pointers pointing back into
other EFI code or data. Interpreting these pointers as romsize leads to
a very large value and if we then try to alloc this amount of memory to
save a copy the alloc call fails.

This leads to a "Failed to alloc mem for rom" error being printed on the
EFI console for each PCI device.

This commit avoids the printing of these errors, by checking romsize
before doing the alloc and if it is larger then 256M silently ignore the
ROM fields instead of trying to alloc mem and fail.

Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
---
 arch/x86/boot/compressed/eboot.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index 886a9115af62..f744b037d3cd 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -230,7 +230,13 @@ __setup_efi_pci64(efi_pci_io_protocol_64 *pci, struct pci_setup_rom **__rom)
 	if (status != EFI_SUCCESS)
 		return status;
 
-	if (!pci->romimage || !pci->romsize)
+	/*
+	 * Some firmwares contain EFI function pointers at the place where the
+	 * romimage and romsize fields are supposed to be. Typically the EFI
+	 * code is mapped at high addresses, translating to an unrealistically
+	 * large romsize. We reject any roms over 256M in size to catch this.
+	 */
+	if (!pci->romimage || !pci->romsize || pci->romsize > 0x10000000)
 		return EFI_INVALID_PARAMETER;
 
 	size = pci->romsize + sizeof(*rom);
-- 
2.17.0.rc2

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