Commit 177366bf authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

bpf: change x86 JITed program stack layout 



in order to JIT programs with different stack sizes we need to
make epilogue and exception path to be stack size independent,
hence move auxiliary stack space from the bottom of the stack
to the top of the stack.
Nice side effect is that JITed function prologue becomes shorter
due to imm8 offset encoding vs imm32.

Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b870aa90

arch/x86/net/bpf_jit.S

+9 −11
Original line number Diff line number Diff line
@@ -19,9 +19,6 @@ 
 */

#define SKBDATA	%r10

#define SKF_MAX_NEG_OFF    $(-0x200000) /* SKF_LL_OFF from filter.h */

#define MAX_BPF_STACK (512 /* from filter.h */ + \

	32 /* space for rbx,r13,r14,r15 */ + \

	8 /* space for skb_copy_bits */)



#define FUNC(name) \

	.globl name; \
@@ -66,7 +63,7 @@ FUNC(sk_load_byte_positive_offset) 


/* rsi contains offset and can be scratched */

#define bpf_slow_path_common(LEN)		\

	lea	-MAX_BPF_STACK + 32(%rbp), %rdx;\

	lea	32(%rbp), %rdx;\

	FRAME_BEGIN;				\

	mov	%rbx, %rdi; /* arg1 == skb */	\

	push	%r9;				\
@@ -83,14 +80,14 @@ FUNC(sk_load_byte_positive_offset) 
bpf_slow_path_word:

	bpf_slow_path_common(4)

	js	bpf_error

	mov	- MAX_BPF_STACK + 32(%rbp),%eax

	mov	32(%rbp),%eax

	bswap	%eax

	ret



bpf_slow_path_half:

	bpf_slow_path_common(2)

	js	bpf_error

	mov	- MAX_BPF_STACK + 32(%rbp),%ax

	mov	32(%rbp),%ax

	rol	$8,%ax

	movzwl	%ax,%eax

	ret
@@ -98,7 +95,7 @@ bpf_slow_path_half: 
bpf_slow_path_byte:

	bpf_slow_path_common(1)

	js	bpf_error

	movzbl	- MAX_BPF_STACK + 32(%rbp),%eax

	movzbl	32(%rbp),%eax

	ret



#define sk_negative_common(SIZE)				\
@@ -148,9 +145,10 @@ FUNC(sk_load_byte_negative_offset) 
bpf_error:

# force a return 0 from jit handler

	xor	%eax,%eax

	mov	- MAX_BPF_STACK(%rbp),%rbx

	mov	- MAX_BPF_STACK + 8(%rbp),%r13

	mov	- MAX_BPF_STACK + 16(%rbp),%r14

	mov	- MAX_BPF_STACK + 24(%rbp),%r15

	mov	(%rbp),%rbx

	mov	8(%rbp),%r13

	mov	16(%rbp),%r14

	mov	24(%rbp),%r15

	add	$40, %rbp

	leaveq

	ret

arch/x86/net/bpf_jit_comp.c

+31 −27
Original line number Diff line number Diff line
@@ -197,12 +197,11 @@ struct jit_context { 
#define BPF_MAX_INSN_SIZE	128

#define BPF_INSN_SAFETY		64



#define STACKSIZE \

	(MAX_BPF_STACK + \

	 32 /* space for rbx, r13, r14, r15 */ + \

#define AUX_STACK_SPACE \

	(32 /* space for rbx, r13, r14, r15 */ + \

	 8 /* space for skb_copy_bits() buffer */)



#define PROLOGUE_SIZE 48

#define PROLOGUE_SIZE 37



/* emit x64 prologue code for BPF program and check it's size.

 * bpf_tail_call helper will skip it while jumping into another program
@@ -215,13 +214,16 @@ static void emit_prologue(u8 **pprog) 
	EMIT1(0x55); /* push rbp */

	EMIT3(0x48, 0x89, 0xE5); /* mov rbp,rsp */



	/* sub rsp, STACKSIZE */

	EMIT3_off32(0x48, 0x81, 0xEC, STACKSIZE);

	/* sub rsp, MAX_BPF_STACK + AUX_STACK_SPACE */

	EMIT3_off32(0x48, 0x81, 0xEC, MAX_BPF_STACK + AUX_STACK_SPACE);



	/* sub rbp, AUX_STACK_SPACE */

	EMIT4(0x48, 0x83, 0xED, AUX_STACK_SPACE);



	/* all classic BPF filters use R6(rbx) save it */



	/* mov qword ptr [rbp-X],rbx */

	EMIT3_off32(0x48, 0x89, 0x9D, -STACKSIZE);

	/* mov qword ptr [rbp+0],rbx */

	EMIT4(0x48, 0x89, 0x5D, 0);



	/* bpf_convert_filter() maps classic BPF register X to R7 and uses R8

	 * as temporary, so all tcpdump filters need to spill/fill R7(r13) and
@@ -231,12 +233,12 @@ static void emit_prologue(u8 **pprog) 
	 * than synthetic ones. Therefore not worth adding complexity.

	 */



	/* mov qword ptr [rbp-X],r13 */

	EMIT3_off32(0x4C, 0x89, 0xAD, -STACKSIZE + 8);

	/* mov qword ptr [rbp-X],r14 */

	EMIT3_off32(0x4C, 0x89, 0xB5, -STACKSIZE + 16);

	/* mov qword ptr [rbp-X],r15 */

	EMIT3_off32(0x4C, 0x89, 0xBD, -STACKSIZE + 24);

	/* mov qword ptr [rbp+8],r13 */

	EMIT4(0x4C, 0x89, 0x6D, 8);

	/* mov qword ptr [rbp+16],r14 */

	EMIT4(0x4C, 0x89, 0x75, 16);

	/* mov qword ptr [rbp+24],r15 */

	EMIT4(0x4C, 0x89, 0x7D, 24);



	/* Clear the tail call counter (tail_call_cnt): for eBPF tail calls

	 * we need to reset the counter to 0. It's done in two instructions,
@@ -246,8 +248,8 @@ static void emit_prologue(u8 **pprog) 


	/* xor eax, eax */

	EMIT2(0x31, 0xc0);

	/* mov qword ptr [rbp-X], rax */

	EMIT3_off32(0x48, 0x89, 0x85, -STACKSIZE + 32);

	/* mov qword ptr [rbp+32], rax */

	EMIT4(0x48, 0x89, 0x45, 32);



	BUILD_BUG_ON(cnt != PROLOGUE_SIZE);

	*pprog = prog;
@@ -289,13 +291,13 @@ static void emit_bpf_tail_call(u8 **pprog) 
	/* if (tail_call_cnt > MAX_TAIL_CALL_CNT)

	 *   goto out;

	 */

	EMIT2_off32(0x8B, 0x85, -STACKSIZE + 36); /* mov eax, dword ptr [rbp - 516] */

	EMIT2_off32(0x8B, 0x85, 36);              /* mov eax, dword ptr [rbp + 36] */

	EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT);     /* cmp eax, MAX_TAIL_CALL_CNT */

#define OFFSET2 36

	EMIT2(X86_JA, OFFSET2);                   /* ja out */

	label2 = cnt;

	EMIT3(0x83, 0xC0, 0x01);                  /* add eax, 1 */

	EMIT2_off32(0x89, 0x85, -STACKSIZE + 36); /* mov dword ptr [rbp - 516], eax */

	EMIT2_off32(0x89, 0x85, 36);              /* mov dword ptr [rbp + 36], eax */



	/* prog = array->ptrs[index]; */

	EMIT4_off32(0x48, 0x8D, 0x84, 0xD6,       /* lea rax, [rsi + rdx * 8 + offsetof(...)] */
@@ -1036,15 +1038,17 @@ common_load: 
			seen_exit = true;

			/* update cleanup_addr */

			ctx->cleanup_addr = proglen;

			/* mov rbx, qword ptr [rbp-X] */

			EMIT3_off32(0x48, 0x8B, 0x9D, -STACKSIZE);

			/* mov r13, qword ptr [rbp-X] */

			EMIT3_off32(0x4C, 0x8B, 0xAD, -STACKSIZE + 8);

			/* mov r14, qword ptr [rbp-X] */

			EMIT3_off32(0x4C, 0x8B, 0xB5, -STACKSIZE + 16);

			/* mov r15, qword ptr [rbp-X] */

			EMIT3_off32(0x4C, 0x8B, 0xBD, -STACKSIZE + 24);



			/* mov rbx, qword ptr [rbp+0] */

			EMIT4(0x48, 0x8B, 0x5D, 0);

			/* mov r13, qword ptr [rbp+8] */

			EMIT4(0x4C, 0x8B, 0x6D, 8);

			/* mov r14, qword ptr [rbp+16] */

			EMIT4(0x4C, 0x8B, 0x75, 16);

			/* mov r15, qword ptr [rbp+24] */

			EMIT4(0x4C, 0x8B, 0x7D, 24);



			/* add rbp, AUX_STACK_SPACE */

			EMIT4(0x48, 0x83, 0xC5, AUX_STACK_SPACE);

			EMIT1(0xC9); /* leave */

			EMIT1(0xC3); /* ret */

			break;

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