From 19f4e715f6659cd85dd7125fc4612a11d23a21bc Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Fri, 14 Mar 2025 12:03:33 +0100 Subject: [PATCH] efi/libstub: Avoid physical address 0x0 when doing random allocation commit cb16dfed0093217a68c0faa9394fa5823927e04c upstream. 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. Cc: Reported-by: Ben Schneider Tested-by: Ben Schneider Reviewed-by: Ilias Apalodimas Signed-off-by: Ard Biesheuvel Signed-off-by: Greg Kroah-Hartman --- drivers/firmware/efi/libstub/randomalloc.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/firmware/efi/libstub/randomalloc.c b/drivers/firmware/efi/libstub/randomalloc.c index 8ad3efb9b1ff..593e98e3b993 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 */