linux-kernel - [PATCH 5.16 28/53] arm64: entry: Add non-kpti __bp_harden_el1

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Date:   Thu, 10 Mar 2022 15:09:33 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>
Subject: [PATCH 5.16 28/53] arm64: entry: Add non-kpti __bp_harden_el1_vectors for mitigations

From: James Morse <james.morse@....com>

commit aff65393fa1401e034656e349abd655cfe272de0 upstream.

kpti is an optional feature, for systems not using kpti a set of
vectors for the spectre-bhb mitigations is needed.

Add another set of vectors, __bp_harden_el1_vectors, that will be
used if a mitigation is needed and kpti is not in use.

The EL1 ventries are repeated verbatim as there is no additional
work needed for entry from EL1.

Reviewed-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: James Morse <james.morse@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm64/kernel/entry.S |   35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -649,10 +649,11 @@ alternative_else_nop_endif
 	.macro tramp_ventry, vector_start, regsize, kpti
 	.align	7
 1:
-	.if	\kpti == 1
 	.if	\regsize == 64
 	msr	tpidrro_el0, x30	// Restored in kernel_ventry
 	.endif
+
+	.if	\kpti == 1
 	/*
 	 * Defend against branch aliasing attacks by pushing a dummy
 	 * entry onto the return stack and using a RET instruction to
@@ -740,6 +741,38 @@ SYM_DATA_END(__entry_tramp_data_start)
 #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
 
 /*
+ * Exception vectors for spectre mitigations on entry from EL1 when
+ * kpti is not in use.
+ */
+	.macro generate_el1_vector
+.Lvector_start\@:
+	kernel_ventry	1, t, 64, sync		// Synchronous EL1t
+	kernel_ventry	1, t, 64, irq		// IRQ EL1t
+	kernel_ventry	1, t, 64, fiq		// FIQ EL1h
+	kernel_ventry	1, t, 64, error		// Error EL1t
+
+	kernel_ventry	1, h, 64, sync		// Synchronous EL1h
+	kernel_ventry	1, h, 64, irq		// IRQ EL1h
+	kernel_ventry	1, h, 64, fiq		// FIQ EL1h
+	kernel_ventry	1, h, 64, error		// Error EL1h
+
+	.rept	4
+	tramp_ventry	.Lvector_start\@, 64, kpti=0
+	.endr
+	.rept 4
+	tramp_ventry	.Lvector_start\@, 32, kpti=0
+	.endr
+	.endm
+
+	.pushsection ".entry.text", "ax"
+	.align	11
+SYM_CODE_START(__bp_harden_el1_vectors)
+	generate_el1_vector
+SYM_CODE_END(__bp_harden_el1_vectors)
+	.popsection
+
+
+/*
  * Register switch for AArch64. The callee-saved registers need to be saved
  * and restored. On entry:
  *   x0 = previous task_struct (must be preserved across the switch)