linux-kernel - [stable:PATCH v4.9.309 32/43] arm64: entry: Make the kpti trampoline's kpti sequence optional

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Message-Id: <20220406164546.1888528-32-james.morse@arm.com>
Date:   Wed,  6 Apr 2022 17:45:35 +0100
From:   James Morse <james.morse@....com>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     James Morse <james.morse@....com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: [stable:PATCH v4.9.309 32/43] arm64: entry: Make the kpti trampoline's kpti sequence optional

commit c47e4d04ba0f1ea17353d85d45f611277507e07a upstream.

Spectre-BHB needs to add sequences to the vectors. Having one global
set of vectors is a problem for big/little systems where the sequence
is costly on cpus that are not vulnerable.

Making the vectors per-cpu in the style of KVM's bh_harden_hyp_vecs
requires the vectors to be generated by macros.

Make the kpti re-mapping of the kernel optional, so the macros can be
used without kpti.

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>
---
 arch/arm64/kernel/entry.S | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 9132400d6a9d..6e1d02d87d45 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -921,9 +921,10 @@ __ni_sys_trace:
 	sub	\dst, \dst, PAGE_SIZE
 	.endm
 
-	.macro tramp_ventry, vector_start, regsize
+	.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
@@ -945,8 +946,12 @@ __ni_sys_trace:
 #endif
 	prfm	plil1strm, [x30, #(1b - \vector_start)]
 	msr	vbar_el1, x30
+	isb
+	.else
+	ldr	x30, =vectors
+	.endif // \kpti == 1
+
 	add	x30, x30, #(1b - \vector_start + 4)
-	isb
 	ret
 .org 1b + 128	// Did we overflow the ventry slot?
 	.endm
@@ -963,15 +968,15 @@ __ni_sys_trace:
 	eret
 	.endm
 
-	.macro	generate_tramp_vector
+	.macro	generate_tramp_vector,	kpti
 .Lvector_start\@:
 	.space	0x400
 
 	.rept	4
-	tramp_ventry	.Lvector_start\@, 64
+	tramp_ventry	.Lvector_start\@, 64, \kpti
 	.endr
 	.rept	4
-	tramp_ventry	.Lvector_start\@, 32
+	tramp_ventry	.Lvector_start\@, 32, \kpti
 	.endr
 	.endm
 
@@ -982,7 +987,7 @@ __ni_sys_trace:
 	.pushsection ".entry.tramp.text", "ax"
 	.align	11
 ENTRY(tramp_vectors)
-	generate_tramp_vector
+	generate_tramp_vector	kpti=1
 END(tramp_vectors)
 
 ENTRY(tramp_exit_native)
-- 
2.30.2