On Mon, 11 Nov 2024 at 22:45, Nicolas Saenz Julienne nsaenz@amazon.com wrote:

Kexec bypasses EFI's switch to virtual mode. In exchange, it has its own routine, kexec_enter_virtual_mode(), that replays the mappings made by the original kernel. Unfortunately, the function fails to reinstate EFI's memory attributes and runtime memory protections, which would've otherwise been set after entering virtual mode. Remediate this by calling efi_runtime_update_mappings() from it.

Cc: stable@vger.kernel.org Fixes: 18141e89a76c ("x86/efi: Add support for EFI_MEMORY_ATTRIBUTES_TABLE") Signed-off-by: Nicolas Saenz Julienne nsaenz@amazon.com

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Notes:

• I tested the Memory Attributes path using QEMU/OVMF.

• Although care is taken to make sure the memory backing the EFI Memory Attributes table is preserved during runtime and reachable after kexec (see efi_memattr_init()). I don't see the same happening for the EFI properties table. Maybe it's just unnecessary as there's an assumption that the table will fall in memory preserved during runtime? Or for another reason? Otherwise, we'd need to make sure it isn't possible to set EFI_NX_PE_DATA on kexec.

arch/x86/platform/efi/efi.c | 1 + 1 file changed, 1 insertion(+)

Thanks.

I think we should just drop support for the EFI_PROPERTIES_TABLE - it was a failed, short-lived experiment that broke the boot on both Linux and Windows, and was replaced with the memory attributes table shortly after.

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c index 88a96816de9a..b9b17892c495 100644 --- a/arch/x86/platform/efi/efi.c +++ b/arch/x86/platform/efi/efi.c @@ -784,6 +784,7 @@ static void __init kexec_enter_virtual_mode(void)

    efi_sync_low_kernel_mappings();
    efi_native_runtime_setup();

•   efi_runtime_update_mappings();
  

#endif }

-- 2.40.1