linux-hardening - [PATCH v4 21/26] efi/x86: Explicitly set sections memory attributes

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Message-Id: <c38ad7a1b89aff743d4a29882a7022d97d4fea58.1671098103.git.baskov@ispras.ru>
Date:   Thu, 15 Dec 2022 15:38:12 +0300
From:   Evgeniy Baskov <baskov@...ras.ru>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Evgeniy Baskov <baskov@...ras.ru>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Peter Jones <pjones@...hat.com>,
        "Limonciello, Mario" <mario.limonciello@....com>,
        joeyli <jlee@...e.com>, lvc-project@...uxtesting.org,
        x86@...nel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v4 21/26] efi/x86: Explicitly set sections memory attributes

Explicitly change sections memory attributes in efi_pe_entry in case
of incorrect EFI implementations and to reduce access rights to
compressed kernel blob. By default it is set executable due to
restriction in maximum number of sections that can fit before zero
page.

Tested-by: Peter Jones <pjones@...hat.com>
Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
---
 drivers/firmware/efi/libstub/x86-stub.c | 54 +++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 1f0a2e7075c3..60697fcd8950 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -27,6 +27,12 @@ const efi_dxe_services_table_t *efi_dxe_table;
 u32 image_offset __section(".data");
 static efi_loaded_image_t *image __section(".data");
 
+extern char _head[], _ehead[];
+extern char _compressed[], _ecompressed[];
+extern char _text[], _etext[];
+extern char _rodata[], _erodata[];
+extern char _data[];
+
 static efi_status_t
 preserve_pci_rom_image(efi_pci_io_protocol_t *pci, struct pci_setup_rom **__rom)
 {
@@ -343,6 +349,52 @@ void __noreturn efi_exit(efi_handle_t handle, efi_status_t status)
 		asm("hlt");
 }
 
+
+/*
+ * Manually setup memory protection attributes for each ELF section
+ * since we cannot do it properly by using PE sections.
+ */
+static void setup_sections_memory_protection(unsigned long image_base)
+{
+#ifdef CONFIG_EFI_DXE_MEM_ATTRIBUTES
+	efi_dxe_table = get_efi_config_table(EFI_DXE_SERVICES_TABLE_GUID);
+
+	if (!efi_dxe_table ||
+	    efi_dxe_table->hdr.signature != EFI_DXE_SERVICES_TABLE_SIGNATURE) {
+		efi_warn("Unable to locate EFI DXE services table\n");
+		efi_dxe_table = NULL;
+		return;
+	}
+
+	/* .setup [image_base, _head] */
+	efi_adjust_memory_range_protection(image_base,
+					   (unsigned long)_head - image_base,
+					   EFI_MEMORY_RO | EFI_MEMORY_XP);
+	/* .head.text [_head, _ehead] */
+	efi_adjust_memory_range_protection((unsigned long)_head,
+					   (unsigned long)_ehead - (unsigned long)_head,
+					   EFI_MEMORY_RO);
+	/* .rodata..compressed [_compressed, _ecompressed] */
+	efi_adjust_memory_range_protection((unsigned long)_compressed,
+					   (unsigned long)_ecompressed - (unsigned long)_compressed,
+					   EFI_MEMORY_RO | EFI_MEMORY_XP);
+	/* .text [_text, _etext] */
+	efi_adjust_memory_range_protection((unsigned long)_text,
+					   (unsigned long)_etext - (unsigned long)_text,
+					   EFI_MEMORY_RO);
+	/* .rodata [_rodata, _erodata] */
+	efi_adjust_memory_range_protection((unsigned long)_rodata,
+					   (unsigned long)_erodata - (unsigned long)_rodata,
+					   EFI_MEMORY_RO | EFI_MEMORY_XP);
+	/* .data, .bss [_data, _end] */
+	efi_adjust_memory_range_protection((unsigned long)_data,
+					   (unsigned long)_end - (unsigned long)_data,
+					   EFI_MEMORY_XP);
+#else
+	(void)image_base;
+#endif
+}
+
 void __noreturn efi_stub_entry(efi_handle_t handle,
 			       efi_system_table_t *sys_table_arg,
 			       struct boot_params *boot_params);
@@ -687,6 +739,8 @@ asmlinkage unsigned long efi_main(efi_handle_t handle,
 		efi_dxe_table = NULL;
 	}
 
+	setup_sections_memory_protection(bzimage_addr - image_offset);
+
 #ifdef CONFIG_CMDLINE_BOOL
 	status = efi_parse_options(CONFIG_CMDLINE);
 	if (status != EFI_SUCCESS) {
-- 
2.37.4