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: 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>

diff --git a/arch/s390/net/bpf_jit.h b/arch/s390/net/bpf_jit.h
deleted file mode 100644 (file)
index 7822ea9..0000000
--- a/arch/s390/net/bpf_jit.h
+++ /dev/null
@@ -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 */

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 76ad52a2444416fee76263783411a686c7c9ae2e..8bb738f1b1b65362bab96819c8777233120e8f27 100644 (file)
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -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);