From 0e9a6a26f50f4813ea08a2848b5df70357f05ab4 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Mon, 12 Feb 2018 15:02:10 -0500 Subject: [PATCH] target-arm: A64: Fix handling of rotate in logic_imm_decode_wmask The code in logic_imm_decode_wmask attempts to rotate a mask value within the bottom 'e' bits of the value with mask = (mask >> r) | (mask << (e - r)); This has two issues: * if the element size is 64 then a rotate by zero results in a shift left by 64, which is undefined behaviour * if the element size is smaller than 64 then this will leave junk in the value at bit 'e' and above, which is not valid input to bitfield_replicate(). As it happens, the bits at bit 'e' to '2e - r' are exactly the ones which bitfield_replicate is going to copy in there, so this isn't a "wrong code generated" bug, but it's confusing and if we ever put an assert in bitfield_replicate it would fire on valid guest code. Fix the former by not doing anything if r is zero, and the latter by masking with bitmask64(e). Backports commit e167adc9d9f5df4f8109aecd4552c407fdce094a from qemu --- qemu/target-arm/translate-a64.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/qemu/target-arm/translate-a64.c b/qemu/target-arm/translate-a64.c index 17e75553..d5ff3ad4 100644 --- a/qemu/target-arm/translate-a64.c +++ b/qemu/target-arm/translate-a64.c @@ -2857,7 +2857,10 @@ static bool logic_imm_decode_wmask(uint64_t *result, unsigned int immn, * by r within the element (which is e bits wide)... */ mask = bitmask64(s + 1); - mask = (mask >> r) | (mask << (e - r)); + if (r) { + mask = (mask >> r) | (mask << (e - r)); + mask &= bitmask64(e); + } /* ...then replicate the element over the whole 64 bit value */ mask = bitfield_replicate(mask, e); *result = mask;