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s390/bpf: Describe the frame using a struct instead of constants

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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: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20250624121501.50536-3-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Ilya Leoshkevich
2025-06-24 14:04:28 +02:00
committed by Alexei Starovoitov
parent b2268d550d
commit e26d523edf
2 changed files with 47 additions and 77 deletions
Download Patch File Download Diff File Expand all files Collapse all files

55
arch/s390/net/bpf_jit.h
View File

@@ -1,55 +0,0 @@
/* 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 */

69
arch/s390/net/bpf_jit_comp.c
View File

@@ -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);