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bpf: Support 64-bit pointers to kfuncs

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test_ksyms_module fails to emit a kfunc call targeting a module on
s390x, because the verifier stores the difference between kfunc
address and __bpf_call_base in bpf_insn.imm, which is s32, and modules
are roughly (1 << 42) bytes away from the kernel on s390x.

Fix by keeping BTF id in bpf_insn.imm for BPF_PSEUDO_KFUNC_CALLs,
and storing the absolute address in bpf_kfunc_desc.

Introduce bpf_jit_supports_far_kfunc_call() in order to limit this new
behavior to the s390x JIT. Otherwise other JITs need to be modified,
which is not desired.

Introduce bpf_get_kfunc_addr() instead of exposing both
find_kfunc_desc() and struct bpf_kfunc_desc.

In addition to sorting kfuncs by imm, also sort them by offset, in
order to handle conflicting imms from different modules. Do this on
all architectures in order to simplify code.

Factor out resolving specialized kfuncs (XPD and dynptr) from
fixup_kfunc_call(). This was required in the first place, because
fixup_kfunc_call() uses find_kfunc_desc(), which returns a const
pointer, so it's not possible to modify kfunc addr without stripping
const, which is not nice. It also removes repetition of code like:

	if (bpf_jit_supports_far_kfunc_call())
		desc->addr = func;
	else
		insn->imm = BPF_CALL_IMM(func);

and separates kfunc_desc_tab fixups from kfunc_call fixups.

Suggested-by: Jiri Olsa <olsajiri@gmail.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230412230632.885985-1-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Ilya Leoshkevich 2023-04-13 01:06:32 +02:00 • committed by Alexei Starovoitov
parent c11bd04648
commit 1cf3bfc60f
5 changed files with 110 additions and 40 deletions
Download patch file Download diff file Expand all files Collapse all files

10
include/linux/bpf.h
View file

@ -2295,6 +2295,9 @@ bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog);
const struct btf_func_model *
bpf_jit_find_kfunc_model(const struct bpf_prog *prog,
const struct bpf_insn *insn);
int bpf_get_kfunc_addr(const struct bpf_prog *prog, u32 func_id,
u16 btf_fd_idx, u8 **func_addr);
struct bpf_core_ctx {
struct bpf_verifier_log *log;
const struct btf *btf;
@ -2545,6 +2548,13 @@ bpf_jit_find_kfunc_model(const struct bpf_prog *prog,
return NULL;
}
static inline int
bpf_get_kfunc_addr(const struct bpf_prog *prog, u32 func_id,
u16 btf_fd_idx, u8 **func_addr)
{
return -ENOTSUPP;
}
static inline bool unprivileged_ebpf_enabled(void)
{
return false;