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From:   Rick Edgecombe <rick.p.edgecombe@intel.com>
To:     dave.hansen@intel.com, luto@kernel.org, peterz@infradead.org,
        x86@kernel.org, akpm@linux-foundation.org, keescook@chromium.org,
        shakeelb@google.com, vbabka@suse.cz, rppt@kernel.org
Cc:     Rick Edgecombe <rick.p.edgecombe@intel.com>, linux-mm@kvack.org,
        linux-hardening@vger.kernel.org,
        kernel-hardening@lists.openwall.com, ira.weiny@intel.com,
        dan.j.williams@intel.com, linux-kernel@vger.kernel.org
Subject: [RFC PATCH v2 14/19] x86/efi: Toggle table protections when copying
Date:   Mon, 30 Aug 2021 16:59:22 -0700
Message-Id: <20210830235927.6443-15-rick.p.edgecombe@intel.com>
In-Reply-To: <20210830235927.6443-1-rick.p.edgecombe@intel.com>
References: <20210830235927.6443-1-rick.p.edgecombe@intel.com>
Precedence: bulk

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