Commit ca45c84a authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Alexei Starovoitov
Browse files

bpf: Add bpf_has_frame_pointer() 



Introduce a bpf_has_frame_pointer() helper that unwinders 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.

Acked-by: default avatarSong Liu <song@kernel.org>
Acked-and-tested-by: default avatarAndrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/fd2bc5b4e261a680774b28f6100509fd5ebad2f0.1764818927.git.jpoimboe@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Reviewed-by: default avatarJiri Olsa <jolsa@kernel.org>
parent 189e5deb

arch/x86/net/bpf_jit_comp.c

+12 −0
Original line number Diff line number Diff line
@@ -1678,6 +1678,9 @@ 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.

	 */
@@ -2736,6 +2739,8 @@ 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;
@@ -3325,6 +3330,9 @@ 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 */

	if (im)

		im->ksym.fp_start = prog - (u8 *)rw_image;



	if (!is_imm8(stack_size)) {

		/* sub rsp, stack_size */

		EMIT3_off32(0x48, 0x81, 0xEC, stack_size);
@@ -3462,7 +3470,11 @@ 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 */

	if (im)

		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 */

include/linux/bpf.h

+3 −0
Original line number Diff line number Diff line
@@ -1283,6 +1283,8 @@ 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 {
@@ -1511,6 +1513,7 @@ 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);

kernel/bpf/core.c

+16 −0
Original line number Diff line number Diff line
@@ -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;