kevin/linux
1
Fork 0
Code

bpf, x86, riscv, arm: no_caller_saved_registers for bpf_get_smp_processor_id()

Browse Source 
The function bpf_get_smp_processor_id() is processed in a different
way, depending on the arch:
- on x86 verifier replaces call to bpf_get_smp_processor_id() with a
  sequence of instructions that modify only r0;
- on riscv64 jit replaces call to bpf_get_smp_processor_id() with a
  sequence of instructions that modify only r0;
- on arm64 jit replaces call to bpf_get_smp_processor_id() with a
  sequence of instructions that modify only r0 and tmp registers.

These rewrites satisfy attribute no_caller_saved_registers contract.
Allow rewrite of no_caller_saved_registers patterns for
bpf_get_smp_processor_id() in order to use this function as a canary
for no_caller_saved_registers tests.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240722233844.1406874-4-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
This commit is contained in:
Eduard Zingerman 2024-07-22 16:38:37 -07:00 committed by Andrii Nakryiko
parent 5b5f51bff1
commit 91b7fbf393
2 changed files with 10 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
kernel/bpf/helpers.c
View File

@ -158,6 +158,7 @@ const struct bpf_func_proto bpf_get_smp_processor_id_proto = {
.func = bpf_get_smp_processor_id,
.gpl_only = false,
.ret_type = RET_INTEGER,
.allow_nocsr = true,
};
BPF_CALL_0(bpf_get_numa_node_id)

11
kernel/bpf/verifier.c
View File

@ -16130,7 +16130,14 @@ static u32 helper_nocsr_clobber_mask(const struct bpf_func_proto *fn)
*/
static bool verifier_inlines_helper_call(struct bpf_verifier_env *env, s32 imm)
{
return false;
switch (imm) {
#ifdef CONFIG_X86_64
case BPF_FUNC_get_smp_processor_id:
return env->prog->jit_requested && bpf_jit_supports_percpu_insn();
#endif
default:
return false;
}
}
/* GCC and LLVM define a no_caller_saved_registers function attribute.
@ -20834,7 +20841,7 @@ patch_map_ops_generic:
#if defined(CONFIG_X86_64) && !defined(CONFIG_UML)
/* Implement bpf_get_smp_processor_id() inline. */
if (insn->imm == BPF_FUNC_get_smp_processor_id &&
prog->jit_requested && bpf_jit_supports_percpu_insn()) {
verifier_inlines_helper_call(env, insn->imm)) {
/* BPF_FUNC_get_smp_processor_id inlining is an
* optimization, so if pcpu_hot.cpu_number is ever
* changed in some incompatible and hard to support