linux-kernel - [PATCH v2 4/9] arm64: alternative: Disallow patching instructions using literals

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Date:   Fri, 26 Aug 2016 10:23:13 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     will.deacon@....com, catalin.marinas@....com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        marc.zyngier@....com, mark.rutland@....com,
        ard.biesheuvel@...aro.org,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Andre Przywara <andre.przywara@....com>
Subject: [PATCH v2 4/9] arm64: alternative: Disallow patching instructions using literals

The alternative code patching doesn't check if the replaced instruction
uses a pc relative literal. This could cause silent corruption in the
instruction stream as the instruction will be executed from a different
address than what it was compiled for. Catch all such cases.

Cc: Marc Zyngier <marc.zyngier@....com>
Cc: Andre Przywara <andre.przywara@....com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Suggested-by: Will Deacon <will.deacon@....com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
 arch/arm64/kernel/alternative.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
index d2ee1b2..6b269a9 100644
--- a/arch/arm64/kernel/alternative.c
+++ b/arch/arm64/kernel/alternative.c
@@ -80,6 +80,12 @@ static u32 get_alt_insn(struct alt_instr *alt, u32 *insnptr, u32 *altinsnptr)
 			offset = target - (unsigned long)insnptr;
 			insn = aarch64_set_branch_offset(insn, offset);
 		}
+	} else if (aarch64_insn_uses_literal(insn)) {
+		/*
+		 * Disallow patching unhandled instructions using PC relative
+		 * literal addresses
+		 */
+		BUG();
 	}
 
 	return insn;
-- 
2.7.4