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 <[email protected]>
Cc: Andre Przywara <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Catalin Marinas <[email protected]>
Suggested-by: Will Deacon <[email protected]>
Signed-off-by: Suzuki K Poulose <[email protected]>
Signed-off-by: Will Deacon <[email protected]>

diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
index 4434dabde898b8eb29b98829bdf1f6a29948a776..992918dfbe2db6a64ba01b08df86db8f203640ac 100644 (file)
--- 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;