Introduce a bpf_has_frame_pointer() helper that uwninders can call to determine whether a given instruction pointer is within the valid frame pointer region of a BPF JIT program or trampoline (i.e., after the prologue, before the epilogue).
This will enable livepatch (with the ORC unwinder) to reliably unwind through BPF JIT frames. Signed-off-by: Josh Poimboeuf <[email protected]> --- arch/x86/net/bpf_jit_comp.c | 10 ++++++++++ include/linux/bpf.h | 3 +++ kernel/bpf/core.c | 16 ++++++++++++++++ 3 files changed, 29 insertions(+) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index de5083cb1d37..510e3e62fd2f 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1661,6 +1661,9 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image emit_prologue(&prog, image, stack_depth, bpf_prog_was_classic(bpf_prog), tail_call_reachable, bpf_is_subprog(bpf_prog), bpf_prog->aux->exception_cb); + + bpf_prog->aux->ksym.fp_start = prog - temp; + /* Exception callback will clobber callee regs for its own use, and * restore the original callee regs from main prog's stack frame. */ @@ -2716,6 +2719,8 @@ st: if (is_imm8(insn->off)) pop_r12(&prog); } EMIT1(0xC9); /* leave */ + bpf_prog->aux->ksym.fp_end = prog - temp; + emit_return(&prog, image + addrs[i - 1] + (prog - temp)); break; @@ -3299,6 +3304,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im } EMIT1(0x55); /* push rbp */ EMIT3(0x48, 0x89, 0xE5); /* mov rbp, rsp */ + im->ksym.fp_start = prog - (u8 *)rw_image; + if (!is_imm8(stack_size)) { /* sub rsp, stack_size */ EMIT3_off32(0x48, 0x81, 0xEC, stack_size); @@ -3436,7 +3443,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, -8); emit_ldx(&prog, BPF_DW, BPF_REG_6, BPF_REG_FP, -rbx_off); + EMIT1(0xC9); /* leave */ + im->ksym.fp_end = prog - (u8 *)rw_image; + if (flags & BPF_TRAMP_F_SKIP_FRAME) { /* skip our return address and return to parent */ EMIT4(0x48, 0x83, 0xC4, 8); /* add rsp, 8 */ diff --git a/include/linux/bpf.h b/include/linux/bpf.h index d808253f2e94..e3f56e8443da 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1257,6 +1257,8 @@ struct bpf_ksym { struct list_head lnode; struct latch_tree_node tnode; bool prog; + u32 fp_start; + u32 fp_end; }; enum bpf_tramp_prog_type { @@ -1483,6 +1485,7 @@ void bpf_image_ksym_add(struct bpf_ksym *ksym); void bpf_image_ksym_del(struct bpf_ksym *ksym); void bpf_ksym_add(struct bpf_ksym *ksym); void bpf_ksym_del(struct bpf_ksym *ksym); +bool bpf_has_frame_pointer(unsigned long ip); int bpf_jit_charge_modmem(u32 size); void bpf_jit_uncharge_modmem(u32 size); bool bpf_prog_has_trampoline(const struct bpf_prog *prog); diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index d595fe512498..7cd8382d1152 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -760,6 +760,22 @@ struct bpf_prog *bpf_prog_ksym_find(unsigned long addr) NULL; } +bool bpf_has_frame_pointer(unsigned long ip) +{ + struct bpf_ksym *ksym; + unsigned long offset; + + guard(rcu)(); + + ksym = bpf_ksym_find(ip); + if (!ksym || !ksym->fp_start || !ksym->fp_end) + return false; + + offset = ip - ksym->start; + + return offset >= ksym->fp_start && offset < ksym->fp_end; +} + const struct exception_table_entry *search_bpf_extables(unsigned long addr) { const struct exception_table_entry *e = NULL; -- 2.51.1
