linux-hardening - [PATCH v4 13/26] arm64: head: use relative references to the RELA and RELR tables

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Date:   Mon, 13 Jun 2022 16:45:37 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-hardening@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Brown <broonie@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: [PATCH v4 13/26] arm64: head: use relative references to the RELA and RELR tables

Formerly, we had to access the RELA and RELR tables via the kernel
mapping that was being relocated, and so deriving the start and end
addresses using ADRP/ADD references was not possible, as the relocation
code runs from the ID map.

Now that we map the entire kernel image via the ID map, we can simplify
this, and just load the entries via the ID map as well.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/kernel/head.S        | 13 ++++---------
 arch/arm64/kernel/vmlinux.lds.S | 12 ++++--------
 2 files changed, 8 insertions(+), 17 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 93734c91a29a..f1497f7b4da0 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -757,13 +757,10 @@ SYM_FUNC_START_LOCAL(__relocate_kernel)
 	 * Iterate over each entry in the relocation table, and apply the
 	 * relocations in place.
 	 */
-	ldr	w9, =__rela_offset		// offset to reloc table
-	ldr	w10, =__rela_size		// size of reloc table
-
+	adr_l	x9, __rela_start
+	adr_l	x10, __rela_end
 	mov_q	x11, KIMAGE_VADDR		// default virtual offset
 	add	x11, x11, x23			// actual virtual offset
-	add	x9, x9, x11			// __va(.rela)
-	add	x10, x9, x10			// __va(.rela) + sizeof(.rela)
 
 0:	cmp	x9, x10
 	b.hs	1f
@@ -813,10 +810,8 @@ SYM_FUNC_START_LOCAL(__relocate_kernel)
 	 * __relocate_kernel is called twice with non-zero displacements (i.e.
 	 * if there is both a physical misalignment and a KASLR displacement).
 	 */
-	ldr	w9, =__relr_offset		// offset to reloc table
-	ldr	w10, =__relr_size		// size of reloc table
-	add	x9, x9, x11			// __va(.relr)
-	add	x10, x9, x10			// __va(.relr) + sizeof(.relr)
+	adr_l	x9, __relr_start
+	adr_l	x10, __relr_end
 
 	sub	x15, x23, x24			// delta from previous offset
 	cbz	x15, 7f				// nothing to do if unchanged
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 0ce3a7c9f8c4..45131e354e27 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -257,21 +257,17 @@ SECTIONS
 	HYPERVISOR_RELOC_SECTION
 
 	.rela.dyn : ALIGN(8) {
+		__rela_start = .;
 		*(.rela .rela*)
+		__rela_end = .;
 	}
 
-	__rela_offset	= ABSOLUTE(ADDR(.rela.dyn) - KIMAGE_VADDR);
-	__rela_size	= SIZEOF(.rela.dyn);
-
-#ifdef CONFIG_RELR
 	.relr.dyn : ALIGN(8) {
+		__relr_start = .;
 		*(.relr.dyn)
+		__relr_end = .;
 	}
 
-	__relr_offset	= ABSOLUTE(ADDR(.relr.dyn) - KIMAGE_VADDR);
-	__relr_size	= SIZEOF(.relr.dyn);
-#endif
-
 	. = ALIGN(SEGMENT_ALIGN);
 	__initdata_end = .;
 	__init_end = .;
-- 
2.30.2