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From: Ard Biesheuvel <ardb@kernel.org>
To: linux-efi@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Matthew Garrett <mjg59@google.com>
Subject: [PATCH 20/20] efi/x86: avoid RWX mappings for all of DRAM
Date: Fri,  3 Jan 2020 12:39:53 +0100
Message-ID: <20200103113953.9571-21-ardb@kernel.org> (raw)
In-Reply-To: <20200103113953.9571-1-ardb@kernel.org>

The EFI code creates RWX mappings for all memory regions that are
occupied after the stub completes, and in the mixed mode case, it
even creates RWX mappings for all of the remaining DRAM as well.

Let's try to avoid this, by setting the NX bit for all memory
regions except the ones that are marked as EFI runtime services
code [which means text+rodata+data in practice, so we cannot mark
them read-only right away]

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/platform/efi/efi_64.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 6ec58ff60b56..a974f8a17f73 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -365,10 +365,6 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 	 * as trim_bios_range() will reserve the first page and isolate it away
 	 * from memory allocators anyway.
 	 */
-	pf = _PAGE_RW;
-	if (sev_active())
-		pf |= _PAGE_ENC;
-
 	if (kernel_map_pages_in_pgd(pgd, 0x0, 0x0, 1, pf)) {
 		pr_err("Failed to create 1:1 mapping for the first page!\n");
 		return 1;
@@ -410,6 +406,19 @@ static void __init __map_region(efi_memory_desc_t *md, u64 va)
 	unsigned long pfn;
 	pgd_t *pgd = efi_mm.pgd;
 
+	/*
+	 * EFI_RUNTIME_SERVICES_CODE regions typically cover PE/COFF
+	 * executable images in memory that consist of both R-X and
+	 * RW- sections, so we cannot apply read-only or non-exec
+	 * permissions just yet. However, modern EFI systems provide
+	 * a memory attributes table that describes those sections
+	 * with the appropriate restricted permissions, which are
+	 * applied in efi_runtime_update_mappings() below. All other
+	 * regions can be mapped non-executable at this point.
+	 */
+	if (md->type != EFI_RUNTIME_SERVICES_CODE)
+		flags |= _PAGE_NX;
+
 	if (!(md->attribute & EFI_MEMORY_WB))
 		flags |= _PAGE_PCD;
 
-- 
2.20.1


  parent reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-03 11:39 [GIT PULL 00/20] More EFI updates for v5.6 Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 01/20] efi/libstub: fix boot argument handling in mixed mode entry code Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 02/20] efi/libstub/x86: force 'hidden' visibility for extern declarations Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 03/20] efi/x86: re-disable RT services for 32-bit kernels running on 64-bit EFI Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 04/20] efi/x86: map the entire EFI vendor string before copying it Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 05/20] efi/x86: avoid redundant cast of EFI firmware service pointer Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 06/20] efi/x86: split off some old memmap handling into separate routines Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 07/20] efi/x86: split SetVirtualAddresMap() wrappers into 32 and 64 bit versions Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 08/20] efi/x86: simplify i386 efi_call_phys() firmware call wrapper Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 09/20] efi/x86: simplify 64-bit EFI " Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 10/20] efi/x86: simplify mixed mode " Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 11/20] efi/x86: drop two near identical versions of efi_runtime_init() Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 12/20] efi/x86: clean up efi_systab_init() routine for legibility Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 13/20] efi/x86: don't panic or BUG() on non-critical error conditions Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 14/20] efi/x86: remove unreachable code in kexec_enter_virtual_mode() Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 15/20] efi/x86: Check number of arguments to variadic functions Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 16/20] efi/x86: Allow translating 64-bit arguments for mixed mode calls Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 17/20] efi: Allow disabling PCI busmastering on bridges during boot Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 18/20] x86/mm: fix NX bit clearing issue in kernel_map_pages_in_pgd Ard Biesheuvel
2020-01-03 11:39 ` [PATCH 19/20] efi/x86: don't map the entire kernel text RW for mixed mode Ard Biesheuvel
2020-01-03 11:39 ` Ard Biesheuvel [this message]
2020-01-09  9:37 ` [GIT PULL 00/20] More EFI updates for v5.6 Ard Biesheuvel
2020-01-10 18:13   ` Ingo Molnar
2020-01-13  7:29     ` Ard Biesheuvel

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