CVE-2024-35917

In the Linux kernel, the following vulnerability has been resolved:
s390/bpf: Fix bpf_plt pointer arithmetic Kui-Feng Lee reported a crash on
s390x triggered by the dummy_st_ops/dummy_init_ptr_arg test [1]:
[<0000000000000002>] 0x2 [<00000000009d5cde>]
bpf_struct_ops_test_run+0x156/0x250 [<000000000033145a>]
__sys_bpf+0xa1a/0xd00 [<00000000003319dc>] __s390x_sys_bpf+0x44/0x50
[<0000000000c4382c>] __do_syscall+0x244/0x300 [<0000000000c59a40>]
system_call+0x70/0x98 This is caused by GCC moving memcpy() after
assignments in bpf_jit_plt(), resulting in NULL pointers being written
instead of the return and the target addresses. Looking at the GCC
internals, the reordering is allowed because the alias analysis thinks that
the memcpy() destination and the assignments’ left-hand-sides are based on
different objects: new_plt and bpf_plt_ret/bpf_plt_target respectively, and
therefore they cannot alias. This is in turn due to a violation of the C
standard: When two pointers are subtracted, both shall point to elements of
the same array object, or one past the last element of the array object …
From the C’s perspective, bpf_plt_ret and bpf_plt are distinct objects and
cannot be subtracted. In the practical terms, doing so confuses the GCC’s
alias analysis. The code was written this way in order to let the C side
know a few offsets defined in the assembly. While nice, this is by no means
necessary. Fix the noncompliance by hardcoding these offsets. [1]
https://lore.kernel.org/bpf/[email protected]/