linux-hardening - [PATCH v4 26/26] arm64: kernel: move ID map out of .text mapping

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Date:   Mon, 13 Jun 2022 16:45:50 +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 26/26] arm64: kernel: move ID map out of .text mapping

Reorganize the ID map slightly so that only code that is executed via
the 1:1 mapping remains. This allows to move the ID map out of the .text
segment, given that it no longer needs exec permissions via the kernel
mapping.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/kernel/head.S        | 5 ++++-
 arch/arm64/kernel/vmlinux.lds.S | 2 +-
 arch/arm64/mm/proc.S            | 2 --
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 834afdc1c6ff..eb959d3387b4 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -525,7 +525,7 @@ SYM_FUNC_END(__primary_switched)
  * end early head section, begin head code that is also used for
  * hotplug and needs to have the same protections as the text region
  */
-	.section ".idmap.text","awx"
+	.text
 
 /*
  * Starting from EL2 or EL1, configure the CPU to execute at the highest
@@ -617,6 +617,7 @@ SYM_FUNC_START_LOCAL(set_cpu_boot_mode_flag)
 	ret
 SYM_FUNC_END(set_cpu_boot_mode_flag)
 
+	.section ".idmap.text","awx"
 	/*
 	 * This provides a "holding pen" for platforms to hold all secondary
 	 * cores are held until we're ready for them to initialise.
@@ -658,6 +659,7 @@ SYM_FUNC_START_LOCAL(secondary_startup)
 	br	x8
 SYM_FUNC_END(secondary_startup)
 
+	.text
 SYM_FUNC_START_LOCAL(__secondary_switched)
 	mov	x0, x20
 	bl	set_cpu_boot_mode_flag
@@ -717,6 +719,7 @@ SYM_FUNC_END(__secondary_too_slow)
  * Checks if the selected granule size is supported by the CPU.
  * If it isn't, park the CPU
  */
+	.section ".idmap.text","awx"
 SYM_FUNC_START(__enable_mmu)
 	mrs	x3, ID_AA64MMFR0_EL1
 	ubfx	x3, x3, #ID_AA64MMFR0_TGRAN_SHIFT, 4
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 3830c6c66e46..d51aa4bbd272 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -169,7 +169,6 @@ SECTIONS
 			LOCK_TEXT
 			KPROBES_TEXT
 			HYPERVISOR_TEXT
-			IDMAP_TEXT
 			*(.gnu.warning)
 		. = ALIGN(16);
 		*(.got)			/* Global offset table		*/
@@ -194,6 +193,7 @@ SECTIONS
 		TRAMP_TEXT
 		HIBERNATE_TEXT
 		KEXEC_TEXT
+		IDMAP_TEXT
 	}
 
 	. = ALIGN(SEGMENT_ALIGN);
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 9ffdf1091d97..7b22e2afe8a0 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -107,7 +107,6 @@ SYM_FUNC_END(cpu_do_suspend)
  *
  * x0: Address of context pointer
  */
-	.pushsection ".idmap.text", "awx"
 SYM_FUNC_START(cpu_do_resume)
 	ldp	x2, x3, [x0]
 	ldp	x4, x5, [x0, #16]
@@ -163,7 +162,6 @@ alternative_else_nop_endif
 	isb
 	ret
 SYM_FUNC_END(cpu_do_resume)
-	.popsection
 #endif
 
 	.pushsection ".idmap.text", "awx"
-- 
2.30.2