linux-hardening - [PATCH v2 12/23] x86/boot: Make kernel_add_identity

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Date:   Tue, 25 Oct 2022 17:12:50 +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>, lvc-project@...uxtesting.org,
        x86@...nel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v2 12/23] x86/boot: Make kernel_add_identity_map() a pointer

Convert kernel_add_identity_map() into a function pointer to be able
to provide alternative implementations of this function. Required
to enable calling the code using this function from EFI environment.

Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
---
 arch/x86/boot/compressed/ident_map_64.c |  7 ++++---
 arch/x86/boot/compressed/misc.c         | 24 ++++++++++++++++++++++++
 arch/x86/boot/compressed/misc.h         | 15 +++------------
 3 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index ba5108c58a4e..1aee524d3c2b 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -92,9 +92,9 @@ bool has_nx; /* set in head_64.S */
 /*
  * Adds the specified range to the identity mappings.
  */
-unsigned long kernel_add_identity_map(unsigned long start,
-				      unsigned long end,
-				      unsigned int flags)
+unsigned long kernel_add_identity_map_(unsigned long start,
+				       unsigned long end,
+				       unsigned int flags)
 {
 	int ret;
 
@@ -142,6 +142,7 @@ void initialize_identity_maps(void *rmode)
 	struct setup_data *sd;
 
 	boot_params = rmode;
+	kernel_add_identity_map = kernel_add_identity_map_;
 
 	/* Exclude the encryption mask from __PHYSICAL_MASK */
 	physical_mask &= ~sme_me_mask;
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index aa4a22bc9cf9..c9c235d65d16 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -275,6 +275,22 @@ static void parse_elf(void *output, unsigned long output_len,
 	free(phdrs);
 }
 
+/*
+ * This points to actual implementation of mapping function
+ * for current environment: either EFI API wrapper,
+ * own implementation or dummy implementation below.
+ */
+unsigned long (*kernel_add_identity_map)(unsigned long start,
+					 unsigned long end,
+					 unsigned int flags);
+
+static inline unsigned long kernel_add_identity_map_dummy(unsigned long start,
+							  unsigned long end,
+							  unsigned int flags)
+{
+	return start;
+}
+
 /*
  * The compressed kernel image (ZO), has been moved so that its position
  * is against the end of the buffer used to hold the uncompressed kernel
@@ -312,6 +328,14 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 
 	init_default_io_ops();
 
+	/*
+	 * On 64-bit this pointer is set during page table uninitialization,
+	 * but on 32-bit it remains uninitialized, since paging is disabled.
+	 */
+	if (IS_ENABLED(CONFIG_X86_32))
+		kernel_add_identity_map = kernel_add_identity_map_dummy;
+
+
 	/*
 	 * Detect TDX guest environment.
 	 *
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 38d31bec062d..0076b2845b4b 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -180,18 +180,9 @@ static inline int count_immovable_mem_regions(void) { return 0; }
 #ifdef CONFIG_X86_5LEVEL
 extern unsigned int __pgtable_l5_enabled, pgdir_shift, ptrs_per_p4d;
 #endif
-#ifdef CONFIG_X86_64
-extern unsigned long kernel_add_identity_map(unsigned long start,
-					     unsigned long end,
-					     unsigned int flags);
-#else
-static inline unsigned long kernel_add_identity_map(unsigned long start,
-						    unsigned long end,
-						    unsigned int flags)
-{
-	return start;
-}
-#endif
+extern unsigned long (*kernel_add_identity_map)(unsigned long start,
+						unsigned long end,
+						unsigned int flags);
 /* Used by PAGE_KERN* macros: */
 extern pteval_t __default_kernel_pte_mask;
 
-- 
2.37.4