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List:       kernel-hardening
Subject:    [RFC PATCH v2 14/19] x86/efi: Toggle table protections when copying
From:       Rick Edgecombe <rick.p.edgecombe () intel ! com>
Date:       2021-08-30 23:59:22
Message-ID: 20210830235927.6443-15-rick.p.edgecombe () intel ! com
[Download RAW message or body]

Toggle page table writability when copying page tables in
efi_sync_low_kernel_mappings(). These page tables will not be protected
until after init, but later on they will not be writable.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 arch/x86/platform/efi/efi_64.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 7515e78ef898..7a5c81450fa4 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -116,7 +116,9 @@ void efi_sync_low_kernel_mappings(void)
 	pgd_k = pgd_offset_k(PAGE_OFFSET);
 
 	num_entries = pgd_index(EFI_VA_END) - pgd_index(PAGE_OFFSET);
+	enable_pgtable_write();
 	memcpy(pgd_efi, pgd_k, sizeof(pgd_t) * num_entries);
+	disable_pgtable_write();
 
 	pgd_efi = efi_pgd + pgd_index(EFI_VA_END);
 	pgd_k = pgd_offset_k(EFI_VA_END);
@@ -124,7 +126,9 @@ void efi_sync_low_kernel_mappings(void)
 	p4d_k = p4d_offset(pgd_k, 0);
 
 	num_entries = p4d_index(EFI_VA_END);
+	enable_pgtable_write();
 	memcpy(p4d_efi, p4d_k, sizeof(p4d_t) * num_entries);
+	disable_pgtable_write();
 
 	/*
 	 * We share all the PUD entries apart from those that map the
@@ -139,13 +143,17 @@ void efi_sync_low_kernel_mappings(void)
 	pud_k = pud_offset(p4d_k, 0);
 
 	num_entries = pud_index(EFI_VA_END);
+	enable_pgtable_write();
 	memcpy(pud_efi, pud_k, sizeof(pud_t) * num_entries);
+	disable_pgtable_write();
 
 	pud_efi = pud_offset(p4d_efi, EFI_VA_START);
 	pud_k = pud_offset(p4d_k, EFI_VA_START);
 
 	num_entries = PTRS_PER_PUD - pud_index(EFI_VA_START);
+	enable_pgtable_write();
 	memcpy(pud_efi, pud_k, sizeof(pud_t) * num_entries);
+	disable_pgtable_write();
 }
 
 /*
-- 
2.17.1

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