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[ Upstream commit579d1b3faa] 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:ef3935eeeb("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.