linux-kernel - [PATCH 2/5] arm64: Handle UNDEF in the EL2 stub vectors

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Date:   Thu, 12 Aug 2021 20:02:10 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Rafał Miłecki <zajec5@...il.com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        bcm-kernel-feedback-list@...adcom.com, kernel-team@...roid.com
Subject: [PATCH 2/5] arm64: Handle UNDEF in the EL2 stub vectors

As we want to handle the silly case where HVC has been disabled
from EL3, augment our ability to handle exception at EL2.

Check for unknown exceptions (usually UNDEF) coming from EL2,
and treat them as a failing HVC call into the stubs. While
this isn't great and obviously doesn't catter for the gigantic
range of possible exceptions, it isn't any worse than what we
have today.

Just don't try and use it for anything else.

Signed-off-by: Marc Zyngier <maz@...nel.org>
---
 arch/arm64/kernel/hyp-stub.S | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index 43d212618834..026a34515b21 100644
--- a/arch/arm64/kernel/hyp-stub.S
+++ b/arch/arm64/kernel/hyp-stub.S
@@ -46,7 +46,16 @@ SYM_CODE_END(__hyp_stub_vectors)
 	.align 11
 
 SYM_CODE_START_LOCAL(elx_sync)
-	cmp	x0, #HVC_SET_VECTORS
+	mrs	x4, spsr_el2
+	and	x4, x4, #PSR_MODE_MASK
+	orr	x4, x4, #1
+	cmp	x4, #PSR_MODE_EL2h
+	b.ne	0f
+	mrs	x4, esr_el2
+	eor	x4, x4, #ESR_ELx_IL
+	cbz	x4, el2_undef
+
+0:	cmp	x0, #HVC_SET_VECTORS
 	b.ne	1f
 	msr	vbar_el2, x1
 	b	9f
@@ -71,6 +80,14 @@ SYM_CODE_START_LOCAL(elx_sync)
 
 9:	mov	x0, xzr
 	eret
+
+el2_undef:
+	// Assumes this was a HVC that went really wrong...
+	mrs	x0, elr_el2
+	add	x0, x0, #4
+	msr	elr_el2, x0
+	mov_q	x0, HVC_STUB_ERR
+	eret
 SYM_CODE_END(elx_sync)
 
 // nVHE? No way! Give me the real thing!
-- 
2.30.2