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| author | Peter Zijlstra <peterz@infradead.org> | 2023-12-15 10:12:18 +0100 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2023-12-15 16:25:55 -0800 |
| commit | 4f9087f16651aca4a5f32da840a53f6660f0579a (patch) | |
| tree | 4aae945ff81a7447ed40741a7fc3fce4fbf6fc65 /kernel/bpf | |
| parent | 4382159696c9af67ee047ed55f2dbf05480f52f6 (diff) | |
| download | lwn-4f9087f16651aca4a5f32da840a53f6660f0579a.tar.gz lwn-4f9087f16651aca4a5f32da840a53f6660f0579a.zip | |
x86/cfi,bpf: Fix BPF JIT call
The current BPF call convention is __nocfi, except when it calls !JIT things,
then it calls regular C functions.
It so happens that with FineIBT the __nocfi and C calling conventions are
incompatible. Specifically __nocfi will call at func+0, while FineIBT will have
endbr-poison there, which is not a valid indirect target. Causing #CP.
Notably this only triggers on IBT enabled hardware, which is probably why this
hasn't been reported (also, most people will have JIT on anyway).
Implement proper CFI prologues for the BPF JIT codegen and drop __nocfi for
x86.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20231215092707.345270396@infradead.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf')
| -rw-r--r-- | kernel/bpf/core.c | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index c34513d645c4..5aa6863ac33b 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -121,6 +121,9 @@ struct bpf_prog *bpf_prog_alloc_no_stats(unsigned int size, gfp_t gfp_extra_flag #endif INIT_LIST_HEAD_RCU(&fp->aux->ksym.lnode); +#ifdef CONFIG_FINEIBT + INIT_LIST_HEAD_RCU(&fp->aux->ksym_prefix.lnode); +#endif mutex_init(&fp->aux->used_maps_mutex); mutex_init(&fp->aux->dst_mutex); @@ -683,6 +686,23 @@ void bpf_prog_kallsyms_add(struct bpf_prog *fp) fp->aux->ksym.prog = true; bpf_ksym_add(&fp->aux->ksym); + +#ifdef CONFIG_FINEIBT + /* + * When FineIBT, code in the __cfi_foo() symbols can get executed + * and hence unwinder needs help. + */ + if (cfi_mode != CFI_FINEIBT) + return; + + snprintf(fp->aux->ksym_prefix.name, KSYM_NAME_LEN, + "__cfi_%s", fp->aux->ksym.name); + + fp->aux->ksym_prefix.start = (unsigned long) fp->bpf_func - 16; + fp->aux->ksym_prefix.end = (unsigned long) fp->bpf_func; + + bpf_ksym_add(&fp->aux->ksym_prefix); +#endif } void bpf_prog_kallsyms_del(struct bpf_prog *fp) @@ -691,6 +711,11 @@ void bpf_prog_kallsyms_del(struct bpf_prog *fp) return; bpf_ksym_del(&fp->aux->ksym); +#ifdef CONFIG_FINEIBT + if (cfi_mode != CFI_FINEIBT) + return; + bpf_ksym_del(&fp->aux->ksym_prefix); +#endif } static struct bpf_ksym *bpf_ksym_find(unsigned long addr) |