Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch)

[Jiri Kosina]

The previous patch was for slightly older kernel, and the logic in 
_prologue() is a bit different in 4.15, but the (cofirmed) fix for 
mainline is basically the same:


From: Jiri Kosina <jkosina@xxxxxxx>
Subject: [PATCH] PTI: unbreak EFI old_memmap

old_memmap's efi_call_phys_prolog() calls set_pgd() with swapper PGD that 
has PAGE_USER set, which makes PTI set NX on it, and therefore EFI can't 
execute it's code.

Fix that by forcefully clearing _PAGE_NX from the PGD (this can't be done
by the pgprot API).

_PAGE_NX will be automatically reintroduced in efi_call_phys_epilog(), as 
_set_pgd() will again notice that this is _PAGE_USER, and set _PAGE_NX on 
it.

Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index d87ac96e37ed..2dd15e967c3f 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -135,7 +135,9 @@ pgd_t * __init efi_call_phys_prolog(void)
 				pud[j] = *pud_offset(p4d_k, vaddr);
 			}
 		}
+		pgd_offset_k(pgd * PGDIR_SIZE)->pgd &= ~_PAGE_NX;
 	}
+
 out:
 	__flush_tlb_all();
 

-- 
Jiri Kosina
SUSE Labs