From: Luke Nelson lukenels@cs.washington.edu
[ Upstream commit 579d1b3faa3735e781ff74aac0afd598515dbc63 ]
This patch fixes two issues present in the current function for encoding arm64 logical immediates when using the 32-bit variants of instructions.
First, the code does not correctly reject an all-ones 32-bit immediate, and returns an undefined instruction encoding.
Second, the code incorrectly rejects some 32-bit immediates that are actually encodable as logical immediates. The root cause is that the code uses a default mask of 64-bit all-ones, even for 32-bit immediates. This causes an issue later on when the default mask is used to fill the top bits of the immediate with ones, shown here:
/* * Pattern: 0..01..10..01..1 * * Fill the unused top bits with ones, and check if * the result is a valid immediate (all ones with a * contiguous ranges of zeroes). */ imm |= ~mask; if (!range_of_ones(~imm)) return AARCH64_BREAK_FAULT;
To see the problem, consider an immediate of the form 0..01..10..01..1, where the upper 32 bits are zero, such as 0x80000001. The code checks if ~(imm | ~mask) contains a range of ones: the incorrect mask yields 1..10..01..10..0, which fails the check; the correct mask yields 0..01..10..0, which succeeds.
The fix for both issues is to generate a correct mask based on the instruction immediate size, and use the mask to check for all-ones, all-zeroes, and values wider than the mask.
Currently, arch/arm64/kvm/va_layout.c is the only user of this function, which uses 64-bit immediates and therefore won't trigger these bugs.
We tested the new code against llvm-mc with all 1,302 encodable 32-bit logical immediates and all 5,334 encodable 64-bit logical immediates.
Fixes: ef3935eeebff ("arm64: insn: Add encoder for bitwise operations using literals") Suggested-by: Will Deacon will@kernel.org Co-developed-by: Xi Wang xi.wang@gmail.com Signed-off-by: Xi Wang xi.wang@gmail.com Signed-off-by: Luke Nelson luke.r.nels@gmail.com Reviewed-by: Marc Zyngier maz@kernel.org Link: https://lore.kernel.org/r/20200508181547.24783-2-luke.r.nels@gmail.com Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/kernel/insn.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c index 4a9e773a177f..cc2f3d901c91 100644 --- a/arch/arm64/kernel/insn.c +++ b/arch/arm64/kernel/insn.c @@ -1535,16 +1535,10 @@ static u32 aarch64_encode_immediate(u64 imm, u32 insn) { unsigned int immr, imms, n, ones, ror, esz, tmp; - u64 mask = ~0UL; - - /* Can't encode full zeroes or full ones */ - if (!imm || !~imm) - return AARCH64_BREAK_FAULT; + u64 mask;
switch (variant) { case AARCH64_INSN_VARIANT_32BIT: - if (upper_32_bits(imm)) - return AARCH64_BREAK_FAULT; esz = 32; break; case AARCH64_INSN_VARIANT_64BIT: @@ -1556,6 +1550,12 @@ static u32 aarch64_encode_immediate(u64 imm, return AARCH64_BREAK_FAULT; }
+ mask = GENMASK(esz - 1, 0); + + /* Can't encode full zeroes, full ones, or value wider than the mask */ + if (!imm || imm == mask || imm & ~mask) + return AARCH64_BREAK_FAULT; + /* * Inverse of Replicate(). Try to spot a repeating pattern * with a pow2 stride.