linux-kernel - [PATCH v3 4/9] arm64: alternative: Disallow patching instructions using literals

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Date:   Mon,  5 Sep 2016 10:58:24 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, will.deacon@....com,
        catalin.marinas@....com, marc.zyngier@....com,
        mark.rutland@....com, james.morse@....com,
        ard.biesheuvel@...aro.org, andre.przywara@....com,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: [PATCH v3 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 4434dab..992918d 100644
--- a/arch/arm64/kernel/alternative.c
+++ b/arch/arm64/kernel/alternative.c
@@ -79,6 +79,12 @@ 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