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Commit 292ba5b1 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Greg Kroah-Hartman
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bpf, x64: fix stack layout of JITed bpf code 



[ Upstream commit fe8d9571dc50232b569242fac7ea6332a654f186 ]

Since commit 177366bf the %rbp stopped pointing to %rbp of the
previous stack frame. That broke frame pointer based stack unwinding.
This commit is a partial revert of it.
Note that the location of tail_call_cnt is fixed, since the verifier
enforces MAX_BPF_STACK stack size for programs with tail calls.

Fixes: 177366bf ("bpf: change x86 JITed program stack layout")
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 4c2ce7ad

arch/x86/net/bpf_jit_comp.c

+21 −53
Original line number Diff line number Diff line
@@ -190,9 +190,7 @@ struct jit_context { 
#define BPF_MAX_INSN_SIZE	128

#define BPF_INSN_SAFETY		64



#define AUX_STACK_SPACE		40 /* Space for RBX, R13, R14, R15, tailcnt */



#define PROLOGUE_SIZE		37

#define PROLOGUE_SIZE		20



/*

 * Emit x86-64 prologue code for BPF program and check its size.
@@ -203,44 +201,19 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf) 
	u8 *prog = *pprog;

	int cnt = 0;



	/* push rbp */

	EMIT1(0x55);



	/* mov rbp,rsp */

	EMIT3(0x48, 0x89, 0xE5);



	/* sub rsp, rounded_stack_depth + AUX_STACK_SPACE */

	EMIT3_off32(0x48, 0x81, 0xEC,

		    round_up(stack_depth, 8) + AUX_STACK_SPACE);



	/* sub rbp, AUX_STACK_SPACE */

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



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

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

	/* 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);



	EMIT1(0x55);             /* push rbp */

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

	/* sub rsp, rounded_stack_depth */

	EMIT3_off32(0x48, 0x81, 0xEC, round_up(stack_depth, 8));

	EMIT1(0x53);             /* push rbx */

	EMIT2(0x41, 0x55);       /* push r13 */

	EMIT2(0x41, 0x56);       /* push r14 */

	EMIT2(0x41, 0x57);       /* push r15 */

	if (!ebpf_from_cbpf) {

		/*

		 * 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, resetting RAX register to 0, and moving it

		 * to the counter location.

		 */



		/* xor eax, eax */

		EMIT2(0x31, 0xc0);

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

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



		/* zero init tail_call_cnt */

		EMIT2(0x6a, 0x00);

		BUILD_BUG_ON(cnt != PROLOGUE_SIZE);

	}



	*pprog = prog;

}
@@ -285,13 +258,13 @@ static void emit_bpf_tail_call(u8 **pprog) 
	 * if (tail_call_cnt > MAX_TAIL_CALL_CNT)

	 *	goto out;

	 */

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

	EMIT2_off32(0x8B, 0x85, -36 - MAX_BPF_STACK); /* mov eax, dword ptr [rbp - 548] */

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

#define OFFSET2 (30 + RETPOLINE_RAX_BPF_JIT_SIZE)

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

	label2 = cnt;

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

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

	EMIT2_off32(0x89, 0x85, -36 - MAX_BPF_STACK); /* mov dword ptr [rbp -548], eax */



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

	EMIT4_off32(0x48, 0x8B, 0x84, 0xD6,       /* mov rax, [rsi + rdx * 8 + offsetof(...)] */
@@ -1006,17 +979,12 @@ xadd: if (is_imm8(insn->off)) 
			seen_exit = true;

			/* Update cleanup_addr */

			ctx->cleanup_addr = proglen;

			/* 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);

			if (!bpf_prog_was_classic(bpf_prog))

				EMIT1(0x5B); /* get rid of tail_call_cnt */

			EMIT2(0x41, 0x5F);   /* pop r15 */

			EMIT2(0x41, 0x5E);   /* pop r14 */

			EMIT2(0x41, 0x5D);   /* pop r13 */

			EMIT1(0x5B);         /* pop rbx */

			EMIT1(0xC9);         /* leave */

			EMIT1(0xC3);         /* ret */

			break;