From df448f7e295526128a384695e55622ad9fb712e7 Mon Sep 17 00:00:00 2001
From: James Morse <james.morse@arm.com>
Date: Mon, 28 Feb 2022 17:24:00 +0100
Subject: [PATCH 04/22] arm64: entry: Move the trampoline data page before the
 text page

Git-commit: c091fb6ae059cda563b2a4d93fdbc548ef34e1d6
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
Patch-mainline: Queued in a subsystem tree
References: bsc#1191580 CVE-2022-0001 CVE-2022-000 CVE-2022-23960


The trampoline code has a data page that holds the address of the vectors,
which is unmapped when running in user-space. This ensures that with
CONFIG_RANDOMIZE_BASE, the randomised address of the kernel can't be
discovered until after the kernel has been mapped.

If the trampoline text page is extended to include multiple sets of
vectors, it will be larger than a single page, making it tricky to
find the data page without knowing the size of the trampoline text
pages, which will vary with PAGE_SIZE.

Move the data page to appear before the text page. This allows the
data page to be found without knowing the size of the trampoline text
pages. 'tramp_vectors' is used to refer to the beginning of the
.entry.tramp.text section, do that explicitly.

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
[ removed SDEI for backport ]
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
---
 arch/arm64/include/asm/fixmap.h | 2 +-
 arch/arm64/kernel/entry.S       | 7 ++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
index ec1e6d6fa14cc..c0cfc6d3bf9f8 100644
--- a/arch/arm64/include/asm/fixmap.h
+++ b/arch/arm64/include/asm/fixmap.h
@@ -59,8 +59,8 @@ enum fixed_addresses {
 #endif /* CONFIG_ACPI_APEI_GHES */
 
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
-	FIX_ENTRY_TRAMP_DATA,
 	FIX_ENTRY_TRAMP_TEXT,
+	FIX_ENTRY_TRAMP_DATA,
 #define TRAMP_VALIAS		(__fix_to_virt(FIX_ENTRY_TRAMP_TEXT))
 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
 	__end_of_permanent_fixed_addresses,
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 8d3cb192e9a7b..d7915e79778e0 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -1094,6 +1094,11 @@ alternative_else_nop_endif
 	 */
 	.endm
 
+	.macro tramp_data_page	dst
+	adr	\dst, .entry.tramp.text
+	sub	\dst, \dst, PAGE_SIZE
+	.endm
+
 	.macro tramp_ventry, regsize = 64
 	.align	7
 1:
@@ -1110,7 +1115,7 @@ alternative_else_nop_endif
 2:
 	tramp_map_kernel	x30
 #ifdef CONFIG_RANDOMIZE_BASE
-	adr	x30, tramp_vectors + PAGE_SIZE
+	tramp_data_page		x30
 alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003
 	ldr	x30, [x30]
 #else
-- 
2.34.1