linux-kernel - [PATCH v2 11/12] arm64: BTI: Reset BTYPE when skipping emulated instructions

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Date:   Thu, 10 Oct 2019 19:44:39 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Jones <drjones@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Kristina Martšenko <kristina.martsenko@....com>,
        Mark Brown <broonie@...nel.org>,
        Paul Elliott <paul.elliott@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Richard Henderson <richard.henderson@...aro.org>,
        Sudakshina Das <sudi.das@....com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Amit Kachhap <amit.kachhap@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: [PATCH v2 11/12] arm64: BTI: Reset BTYPE when skipping emulated instructions

Since normal execution of any non-branch instruction resets the
PSTATE BTYPE field to 0, so do the same thing when emulating a
trapped instruction.

Branches don't trap directly, so we should never need to assign a
non-zero value to BTYPE here.

Signed-off-by: Dave Martin <Dave.Martin@....com>
---
 arch/arm64/kernel/traps.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 3af2768..4d8ce50 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -331,6 +331,8 @@ void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
 
 	if (regs->pstate & PSR_MODE32_BIT)
 		advance_itstate(regs);
+	else
+		regs->pstate &= ~(u64)PSR_BTYPE_MASK;
 }
 
 static LIST_HEAD(undef_hook);
-- 
2.1.4