aeecb678ec
[ Upstream commit 114b5b3b4bde7358624437be2f12cde1b265224e ]
A64_LDRSW() takes three registers: Xt, Xn, Xm as arguments and it loads
and sign extends the value at address Xn + Xm into register Xt.
Currently, the offset is being directly used in place of the tmp
register which has the offset already loaded by the last emitted
instruction.
This will cause JIT failures. The easiest way to reproduce this is to
test the following code through test_bpf module:
{
"BPF_LDX_MEMSX | BPF_W",
.u.insns_int = {
BPF_LD_IMM64(R1, 0x00000000deadbeefULL),
BPF_LD_IMM64(R2, 0xffffffffdeadbeefULL),
BPF_STX_MEM(BPF_DW, R10, R1, -7),
BPF_LDX_MEMSX(BPF_W, R0, R10, -7),
BPF_JMP_REG(BPF_JNE, R0, R2, 1),
BPF_ALU64_IMM(BPF_MOV, R0, 0),
BPF_EXIT_INSN(),
},
INTERNAL,
{ },
{ { 0, 0 } },
.stack_depth = 7,
},
We need to use the offset as -7 to trigger this code path, there could
be other valid ways to trigger this from proper BPF programs as well.
This code is rejected by the JIT because -7 is passed to A64_LDRSW() but
it expects a valid register (0 - 31).
roott@pjy:~# modprobe test_bpf test_name="BPF_LDX_MEMSX | BPF_W"
[11300.490371] test_bpf: test_bpf: set 'test_bpf' as the default test_suite.
[11300.491750] test_bpf: #345 BPF_LDX_MEMSX | BPF_W
[11300.493179] aarch64_insn_encode_register: unknown register encoding -7
[11300.494133] aarch64_insn_encode_register: unknown register encoding -7
[11300.495292] FAIL to select_runtime err=-524
[11300.496804] test_bpf: Summary: 0 PASSED, 1 FAILED, [0/0 JIT'ed]
modprobe: ERROR: could not insert 'test_bpf': Invalid argument
Applying this patch fixes the issue.
root@pjy:~# modprobe test_bpf test_name="BPF_LDX_MEMSX | BPF_W"
[ 292.837436] test_bpf: test_bpf: set 'test_bpf' as the default test_suite.
[ 292.839416] test_bpf: #345 BPF_LDX_MEMSX | BPF_W jited:1 156 PASS
[ 292.844794] test_bpf: Summary: 1 PASSED, 0 FAILED, [1/1 JIT'ed]
Fixes: cc88f540da52 ("bpf, arm64: Support sign-extension load instructions")
Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Message-ID: <20240312235917.103626-1-puranjay12@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@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.