diff mbox series

efi/libstub: Avoid physical address 0x0 when doing random allocation

Message ID 20250314110845.1559302-2-ardb+git@google.com
State New
Headers show
Series efi/libstub: Avoid physical address 0x0 when doing random allocation | expand

Commit Message

Ard Biesheuvel March 14, 2025, 11:08 a.m. UTC 
From: Ard Biesheuvel <ardb@kernel.org>

Ben reports spurious EFI zboot failures on a system where physical RAM
starts at 0x0. When doing random memory allocation from the EFI stub on
such a platform, a random seed of 0x0 (which means no entropy source is
available) will result in the allocation to be placed at address 0x0 if
sufficient space is available.

When this allocation is subsequently passed on to the decompression
code, the 0x0 address is mistaken for NULL and the code complains and
gives up.

So avoid address 0x0 when doing random allocation, and set the minimum
address to the minimum alignment.

Reported-by: Ben Schneider <ben@bens.haus>
Tested-by: Ben Schneider <ben@bens.haus>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/libstub/randomalloc.c | 4 ++++
 1 file changed, 4 insertions(+)
diff mbox series

Patch

diff --git a/drivers/firmware/efi/libstub/randomalloc.c b/drivers/firmware/efi/libstub/randomalloc.c
index 5a732018be36..fd80b2f3233a 100644
--- a/drivers/firmware/efi/libstub/randomalloc.c
+++ b/drivers/firmware/efi/libstub/randomalloc.c
@@ -75,6 +75,10 @@  efi_status_t efi_random_alloc(unsigned long size,
 	if (align < EFI_ALLOC_ALIGN)
 		align = EFI_ALLOC_ALIGN;
 
+	/* Avoid address 0x0, as it can be mistaken for NULL */
+	if (alloc_min == 0)
+		alloc_min = align;
+
 	size = round_up(size, EFI_ALLOC_ALIGN);
 
 	/* count the suitable slots in each memory map entry */