Commit e26d523e authored by Ilya Leoshkevich's avatar Ilya Leoshkevich Committed by Alexei Starovoitov
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s390/bpf: Describe the frame using a struct instead of constants 



Currently the caller-allocated portion of the stack frame is described
using constants, hardcoded values, and an ASCII drawing, making it
harder than necessary to ensure that everything is in sync.

Declare a struct and use offsetof() and offsetofend() macros to refer
to various values stored within the frame.

Signed-off-by: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20250624121501.50536-3-iii@linux.ibm.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent b2268d55

arch/s390/net/bpf_jit.h

deleted100644 → 0
+0 −55
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

/*

 * BPF Jit compiler defines

 *

 * Copyright IBM Corp. 2012,2015

 *

 * Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>

 *	      Michael Holzheu <holzheu@linux.vnet.ibm.com>

 */



#ifndef __ARCH_S390_NET_BPF_JIT_H

#define __ARCH_S390_NET_BPF_JIT_H



#ifndef __ASSEMBLY__



#include <linux/filter.h>

#include <linux/types.h>



#endif /* __ASSEMBLY__ */



/*

 * Stackframe layout (packed stack):

 *

 *				    ^ high

 *	      +---------------+     |

 *	      | old backchain |     |

 *	      +---------------+     |

 *	      |   r15 - r6    |     |

 *	      +---------------+     |

 *	      | 4 byte align  |     |

 *	      | tail_call_cnt |     |

 * BFP	   -> +===============+     |

 *	      |		      |     |

 *	      |   BPF stack   |     |

 *	      |		      |     |

 * R15+160 -> +---------------+     |

 *	      | new backchain |     |

 * R15+152 -> +---------------+     |

 *	      | + 152 byte SA |     |

 * R15	   -> +---------------+     + low

 *

 * We get 160 bytes stack space from calling function, but only use

 * 12 * 8 byte for old backchain, r15..r6, and tail_call_cnt.

 *

 * The stack size used by the BPF program ("BPF stack" above) is passed

 * via "aux->stack_depth".

 */

#define STK_SPACE_ADD	(160)

#define STK_160_UNUSED	(160 - 12 * 8)

#define STK_OFF		(STK_SPACE_ADD - STK_160_UNUSED)



#define STK_OFF_R6	(160 - 11 * 8)	/* Offset of r6 on stack */

#define STK_OFF_TCCNT	(160 - 12 * 8)	/* Offset of tail_call_cnt on stack */



#endif /* __ARCH_S390_NET_BPF_JIT_H */

arch/s390/net/bpf_jit_comp.c

+47 −22
Original line number Diff line number Diff line
@@ -32,7 +32,6 @@ 
#include <asm/set_memory.h>

#include <asm/text-patching.h>

#include <asm/unwind.h>

#include "bpf_jit.h"



struct bpf_jit {

	u32 seen;		/* Flags to remember seen eBPF instructions */
@@ -54,7 +53,7 @@ struct bpf_jit { 
	int prologue_plt;	/* Start of prologue hotpatch PLT */

	int kern_arena;		/* Pool offset of kernel arena address */

	u64 user_arena;		/* User arena address */

	u32 frame_off;		/* Offset of frame from %r15 */

	u32 frame_off;		/* Offset of struct bpf_prog from %r15 */

};



#define SEEN_MEM	BIT(0)		/* use mem[] for temporary storage */
@@ -426,12 +425,26 @@ static void jit_fill_hole(void *area, unsigned int size) 
	memset(area, 0, size);

}



/*

 * Caller-allocated part of the frame.

 * Thanks to packed stack, its otherwise unused initial part can be used for

 * the BPF stack and for the next frame.

 */

struct prog_frame {

	u64 unused[8];

	/* BPF stack starts here and grows towards 0 */

	u32 tail_call_cnt;

	u32 pad;

	u64 r6[10];  /* r6 - r15 */

	u64 backchain;

} __packed;



/*

 * Save registers from "rs" (register start) to "re" (register end) on stack

 */

static void save_regs(struct bpf_jit *jit, u32 rs, u32 re)

{

	u32 off = STK_OFF_R6 + (rs - 6) * 8;

	u32 off = offsetof(struct prog_frame, r6) + (rs - 6) * 8;



	if (rs == re)

		/* stg %rs,off(%r15) */
@@ -446,7 +459,7 @@ static void save_regs(struct bpf_jit *jit, u32 rs, u32 re) 
 */

static void restore_regs(struct bpf_jit *jit, u32 rs, u32 re)

{

	u32 off = jit->frame_off + STK_OFF_R6 + (rs - 6) * 8;

	u32 off = jit->frame_off + offsetof(struct prog_frame, r6) + (rs - 6) * 8;



	if (rs == re)

		/* lg %rs,off(%r15) */
@@ -570,10 +583,12 @@ static void bpf_jit_plt(struct bpf_plt *plt, void *ret, void *target) 
 * Emit function prologue

 *

 * Save registers and create stack frame if necessary.

 * See stack frame layout description in "bpf_jit.h"!

 * Stack frame layout is described by struct prog_frame.

 */

static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp)

{

	BUILD_BUG_ON(sizeof(struct prog_frame) != STACK_FRAME_OVERHEAD);



	/* No-op for hotpatching */

	/* brcl 0,prologue_plt */

	EMIT6_PCREL_RILC(0xc0040000, 0, jit->prologue_plt);
@@ -581,8 +596,9 @@ static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp) 


	if (!bpf_is_subprog(fp)) {

		/* Initialize the tail call counter in the main program. */

		/* xc STK_OFF_TCCNT(4,%r15),STK_OFF_TCCNT(%r15) */

		_EMIT6(0xd703f000 | STK_OFF_TCCNT, 0xf000 | STK_OFF_TCCNT);

		/* xc tail_call_cnt(4,%r15),tail_call_cnt(%r15) */

		_EMIT6(0xd703f000 | offsetof(struct prog_frame, tail_call_cnt),

		       0xf000 | offsetof(struct prog_frame, tail_call_cnt));

	} else {

		/*

		 * Skip the tail call counter initialization in subprograms.
@@ -625,13 +641,15 @@ static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp) 
	if (is_first_pass(jit) || (jit->seen & SEEN_STACK)) {

		/* lgr %w1,%r15 (backchain) */

		EMIT4(0xb9040000, REG_W1, REG_15);

		/* la %bfp,STK_160_UNUSED(%r15) (BPF frame pointer) */

		EMIT4_DISP(0x41000000, BPF_REG_FP, REG_15, STK_160_UNUSED);

		/* la %bfp,unused_end(%r15) (BPF frame pointer) */

		EMIT4_DISP(0x41000000, BPF_REG_FP, REG_15,

			   offsetofend(struct prog_frame, unused));

		/* aghi %r15,-frame_off */

		EMIT4_IMM(0xa70b0000, REG_15, -jit->frame_off);

		/* stg %w1,152(%r15) (backchain) */

		/* stg %w1,backchain(%r15) */

		EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W1, REG_0,

			      REG_15, 152);

			      REG_15,

			      offsetof(struct prog_frame, backchain));

	}

}
@@ -1774,9 +1792,10 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, 
		 * Note 2: We assume that the verifier does not let us call the

		 * main program, which clears the tail call counter on entry.

		 */

		/* mvc STK_OFF_TCCNT(4,%r15),frame_off+STK_OFF_TCCNT(%r15) */

		_EMIT6(0xd203f000 | STK_OFF_TCCNT,

		       0xf000 | (jit->frame_off + STK_OFF_TCCNT));

		/* mvc tail_call_cnt(4,%r15),frame_off+tail_call_cnt(%r15) */

		_EMIT6(0xd203f000 | offsetof(struct prog_frame, tail_call_cnt),

		       0xf000 | (jit->frame_off +

				 offsetof(struct prog_frame, tail_call_cnt)));



		/* Sign-extend the kfunc arguments. */

		if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
@@ -1827,7 +1846,8 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, 
		 *         goto out;

		 */



		off = jit->frame_off + STK_OFF_TCCNT;

		off = jit->frame_off +

		      offsetof(struct prog_frame, tail_call_cnt);

		/* lhi %w0,1 */

		EMIT4_IMM(0xa7080000, REG_W0, 1);

		/* laal %w1,%w0,off(%r15) */
@@ -2160,7 +2180,9 @@ static int bpf_jit_prog(struct bpf_jit *jit, struct bpf_prog *fp, 
	jit->prg = 0;

	jit->excnt = 0;

	if (is_first_pass(jit) || (jit->seen & SEEN_STACK))

		jit->frame_off = STK_OFF + round_up(fp->aux->stack_depth, 8);

		jit->frame_off = sizeof(struct prog_frame) -

				 offsetofend(struct prog_frame, unused) +

				 round_up(fp->aux->stack_depth, 8);

	else

		jit->frame_off = 0;
@@ -2642,9 +2664,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, 
	/* stg %r1,backchain_off(%r15) */

	EMIT6_DISP_LH(0xe3000000, 0x0024, REG_1, REG_0, REG_15,

		      tjit->backchain_off);

	/* mvc tccnt_off(4,%r15),stack_size+STK_OFF_TCCNT(%r15) */

	/* mvc tccnt_off(4,%r15),stack_size+tail_call_cnt(%r15) */

	_EMIT6(0xd203f000 | tjit->tccnt_off,

	       0xf000 | (tjit->stack_size + STK_OFF_TCCNT));

	       0xf000 | (tjit->stack_size +

			 offsetof(struct prog_frame, tail_call_cnt)));

	/* stmg %r2,%rN,fwd_reg_args_off(%r15) */

	if (nr_reg_args)

		EMIT6_DISP_LH(0xeb000000, 0x0024, REG_2,
@@ -2781,8 +2804,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, 
				       (nr_stack_args * sizeof(u64) - 1) << 16 |

				       tjit->stack_args_off,

			       0xf000 | tjit->orig_stack_args_off);

		/* mvc STK_OFF_TCCNT(4,%r15),tccnt_off(%r15) */

		_EMIT6(0xd203f000 | STK_OFF_TCCNT, 0xf000 | tjit->tccnt_off);

		/* mvc tail_call_cnt(4,%r15),tccnt_off(%r15) */

		_EMIT6(0xd203f000 | offsetof(struct prog_frame, tail_call_cnt),

		       0xf000 | tjit->tccnt_off);

		/* lgr %r1,%r8 */

		EMIT4(0xb9040000, REG_1, REG_8);

		/* %r1() */
@@ -2839,8 +2863,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, 
	if (flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET))

		EMIT6_DISP_LH(0xe3000000, 0x0004, REG_2, REG_0, REG_15,

			      tjit->retval_off);

	/* mvc stack_size+STK_OFF_TCCNT(4,%r15),tccnt_off(%r15) */

	_EMIT6(0xd203f000 | (tjit->stack_size + STK_OFF_TCCNT),

	/* mvc stack_size+tail_call_cnt(4,%r15),tccnt_off(%r15) */

	_EMIT6(0xd203f000 | (tjit->stack_size +

			     offsetof(struct prog_frame, tail_call_cnt)),

	       0xf000 | tjit->tccnt_off);

	/* aghi %r15,stack_size */

	EMIT4_IMM(0xa70b0000, REG_15, tjit->stack_size);