On 01.10.24 15:51, Alexandre Ghiti wrote:
Hi Heinrich,
On 29/09/2024 16:02, Heinrich Schuchardt wrote:
The IMAGE_DLLCHARACTERISTICS_NX_COMPAT informs the firmware that the
EFI binary does not rely on pages that are both executable and
writable.
The flag is used by some distro versions of GRUB to decide if the EFI
binary may be executed.
As the Linux kernel neither has RWX sections nor needs RWX pages for
relocation we should set the flag.
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@xxxxxxxxxxxxx>
---
arch/riscv/kernel/efi-header.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/riscv/kernel/efi-header.S b/arch/riscv/kernel/efi-
header.S
index 515b2dfbca75..c5f17c2710b5 100644
--- a/arch/riscv/kernel/efi-header.S
+++ b/arch/riscv/kernel/efi-header.S
@@ -64,7 +64,7 @@ extra_header_fields:
.long efi_header_end - _start // SizeOfHeaders
.long 0 // CheckSum
.short IMAGE_SUBSYSTEM_EFI_APPLICATION // Subsystem
- .short 0 // DllCharacteristics
+ .short IMAGE_DLL_CHARACTERISTICS_NX_COMPAT //
DllCharacteristics
.quad 0 // SizeOfStackReserve
.quad 0 // SizeOfStackCommit
.quad 0 // SizeOfHeapReserve
I don't understand if this fixes something or not: what could go wrong
if we don't do this?
Thanks,
Alex
Hello Alexandre,
https://learn.microsoft.com/en-us/windows-hardware/drivers/bringup/uefi-ca-memory-mitigation-requirements
describes Microsoft's effort to improve security by avoiding memory
pages that are both executable and writable.
IMAGE_DLL_CHARACTERISTICS_NX_COMPAT is an assertion by the EFI binary
that it does not use RWX pages. It may use the
EFI_MEMORY_ATTRIBUTE_PROTOCOL to set whether a page is writable or
executable (but not both).
When using secure boot, compliant firmware will not allow loading a
binary if the flag is not set.
Best regards
Heinrich
