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3b3b84aacb
As reported by Jose E. Marchesi in off-list discussion, GCC and LLVM
generate slightly different code for dummy_st_ops_success/test_1():
SEC("struct_ops/test_1")
int BPF_PROG(test_1, struct bpf_dummy_ops_state *state)
{
int ret;
if (!state)
return 0xf2f3f4f5;
ret = state->val;
state->val = 0x5a;
return ret;
}
GCC-generated LLVM-generated
---------------------------- ---------------------------
0: r1 = *(u64 *)(r1 + 0x0) 0: w0 = -0xd0c0b0b
1: if r1 == 0x0 goto 5f 1: r1 = *(u64 *)(r1 + 0x0)
2: r0 = *(s32 *)(r1 + 0x0) 2: if r1 == 0x0 goto 6f
3: *(u32 *)(r1 + 0x0) = 0x5a 3: r0 = *(u32 *)(r1 + 0x0)
4: exit 4: w2 = 0x5a
5: r0 = -0xd0c0b0b 5: *(u32 *)(r1 + 0x0) = r2
6: exit 6: exit
If the 'state' argument is not marked as nullable in
net/bpf/bpf_dummy_struct_ops.c, the verifier would assume that
'r1 == 0x0' is never true:
- for the GCC version, this means that instructions #5-6 would be
marked as dead and removed;
- for the LLVM version, all instructions would be marked as live.
The test dummy_st_ops/dummy_init_ret_value actually sets the 'state'
parameter to NULL.
Therefore, when the 'state' argument is not marked as nullable,
the GCC-generated version of the code would trigger a NULL pointer
dereference at instruction #3.
This patch updates the test_1() test case to always follow a shape
similar to the GCC-generated version above, in order to verify whether
the 'state' nullability is marked correctly.
Reported-by: Jose E. Marchesi <jemarch@gnu.org>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240424012821.595216-3-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@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
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText 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.