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From: Kalesh Singh <kaleshsingh@google.com>
Cc: kernel-team@android.com,
	Catalin Marinas <catalin.marinas@arm.com>,
	Pasha Tatashin <pasha.tatashin@soleen.com>,
	will@kernel.org, Peter Collingbourne <pcc@google.com>,
	maz@kernel.org, linux-kernel@vger.kernel.org,
	Joey Gouly <joey.gouly@arm.com>,
	kvmarm@lists.cs.columbia.edu, Andrew Walbran <qwandor@google.com>,
	Kalesh Singh <kaleshsingh@google.com>,
	surenb@google.com, linux-arm-kernel@lists.infradead.org
Subject: [PATCH 3/7] arm64: asm: Introduce test_sp_overflow macro
Date: Thu, 10 Feb 2022 14:41:44 -0800	[thread overview]
Message-ID: <20220210224220.4076151-4-kaleshsingh@google.com> (raw)
In-Reply-To: <20220210224220.4076151-1-kaleshsingh@google.com>

From: Quentin Perret <qperret@google.com>

The asm entry code in the kernel uses a trick to check if VMAP'd stacks
have overflowed by aligning them at THREAD_SHIFT * 2 granularity and
checking the SP's THREAD_SHIFT bit.

Protected KVM will soon make use of a similar trick to detect stack
overflows, so factor out the asm code in a re-usable macro.

Signed-off-by: Quentin Perret <qperret@google.com>
[Kalesh - Resolve minor conflicts]
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
---
 arch/arm64/include/asm/assembler.h | 11 +++++++++++
 arch/arm64/kernel/entry.S          |  9 ++-------
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index e8bd0af0141c..ad40eb0eee83 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -850,4 +850,15 @@ alternative_endif
 
 #endif /* GNU_PROPERTY_AARCH64_FEATURE_1_DEFAULT */
 
+/*
+ * Test whether the SP has overflowed, without corrupting a GPR.
+ */
+.macro test_sp_overflow shift, label
+	add	sp, sp, x0			// sp' = sp + x0
+	sub	x0, sp, x0			// x0' = sp' - x0 = (sp + x0) - x0 = sp
+	tbnz	x0, #\shift, \label
+	sub	x0, sp, x0			// x0'' = sp' - x0' = (sp + x0) - sp = x0
+	sub	sp, sp, x0			// sp'' = sp' - x0 = (sp + x0) - x0 = sp
+.endm
+
 #endif	/* __ASM_ASSEMBLER_H */
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 772ec2ecf488..2632bc47b348 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -53,16 +53,11 @@ alternative_else_nop_endif
 	sub	sp, sp, #PT_REGS_SIZE
 #ifdef CONFIG_VMAP_STACK
 	/*
-	 * Test whether the SP has overflowed, without corrupting a GPR.
 	 * Task and IRQ stacks are aligned so that SP & (1 << THREAD_SHIFT)
 	 * should always be zero.
 	 */
-	add	sp, sp, x0			// sp' = sp + x0
-	sub	x0, sp, x0			// x0' = sp' - x0 = (sp + x0) - x0 = sp
-	tbnz	x0, #THREAD_SHIFT, 0f
-	sub	x0, sp, x0			// x0'' = sp' - x0' = (sp + x0) - sp = x0
-	sub	sp, sp, x0			// sp'' = sp' - x0 = (sp + x0) - x0 = sp
-	b	el\el\ht\()_\regsize\()_\label
+	test_sp_overflow THREAD_SHIFT, 0f
+	b       el\el\ht\()_\regsize\()_\label
 
 0:
 	/*
-- 
2.35.1.265.g69c8d7142f-goog

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  parent reply	other threads:[~2022-02-11  9:28 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-10 22:41 [PATCH 0/7] KVM: arm64: Hypervisor stack enhancements Kalesh Singh
2022-02-10 22:41 ` [PATCH 1/7] KVM: arm64: Map the stack pages in the 'private' range Kalesh Singh
2022-02-10 22:41 ` [PATCH 2/7] KVM: arm64: Factor out private range VA allocation Kalesh Singh
2022-02-10 22:41 ` Kalesh Singh [this message]
2022-02-10 22:41 ` [PATCH 4/7] KVM: arm64: Allocate guard pages near hyp stacks Kalesh Singh
2022-02-14 14:06   ` Marc Zyngier
2022-02-14 22:03     ` Kalesh Singh
2022-02-10 22:41 ` [PATCH 5/7] KVM: arm64: Add Hyp overflow stack Kalesh Singh
2022-02-10 22:41 ` [PATCH 6/7] KVM: arm64: Unwind and dump nVHE HYP stacktrace Kalesh Singh
2022-02-10 22:41 ` [PATCH 7/7] KVM: arm64: Symbolize the nVHE HYP backtrace Kalesh Singh
2022-02-14 11:41 ` [PATCH 0/7] KVM: arm64: Hypervisor stack enhancements Marc Zyngier
2022-02-14 21:54   ` Kalesh Singh

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