Hi,
As discussed in [1], here are the backports of the s390 BPF tail counter fixes. Commits 1-2 are NFC prerequisites, commits 3-4 are fixes themselves.
[1] https://lore.kernel.org/stable/CA+G9fYsdErtgqKuyPfFhMS9haGKavBVCHQnipv2EeXM3...
Best regards, Ilya
Ilya Leoshkevich (4): s390/bpf: Centralize frame offset calculations s390/bpf: Describe the frame using a struct instead of constants s390/bpf: Write back tail call counter for BPF_PSEUDO_CALL s390/bpf: Write back tail call counter for BPF_TRAMP_F_CALL_ORIG
arch/s390/net/bpf_jit.h | 55 -------------- arch/s390/net/bpf_jit_comp.c | 139 ++++++++++++++++++++++------------- 2 files changed, 86 insertions(+), 108 deletions(-) delete mode 100644 arch/s390/net/bpf_jit.h
commit b2268d550d20ff860bddfe3a91b1aec00414689a upstream.
The calculation of the distance from %r15 to the caller-allocated portion of the stack frame is copy-pasted into multiple places in the JIT code.
Move it to bpf_jit_prog() and save the result into bpf_jit::frame_off, so that the other parts of the JIT can use it.
Signed-off-by: Ilya Leoshkevich iii@linux.ibm.com Link: https://lore.kernel.org/r/20250624121501.50536-2-iii@linux.ibm.com Signed-off-by: Alexei Starovoitov ast@kernel.org --- arch/s390/net/bpf_jit_comp.c | 56 +++++++++++++++++------------------- 1 file changed, 26 insertions(+), 30 deletions(-)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c index ead8d9ba9032c..12fda05aadf61 100644 --- a/arch/s390/net/bpf_jit_comp.c +++ b/arch/s390/net/bpf_jit_comp.c @@ -56,6 +56,7 @@ 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 */ };
#define SEEN_MEM BIT(0) /* use mem[] for temporary storage */ @@ -421,12 +422,9 @@ static void save_regs(struct bpf_jit *jit, u32 rs, u32 re) /* * Restore registers from "rs" (register start) to "re" (register end) on stack */ -static void restore_regs(struct bpf_jit *jit, u32 rs, u32 re, u32 stack_depth) +static void restore_regs(struct bpf_jit *jit, u32 rs, u32 re) { - u32 off = STK_OFF_R6 + (rs - 6) * 8; - - if (jit->seen & SEEN_STACK) - off += STK_OFF + stack_depth; + u32 off = jit->frame_off + STK_OFF_R6 + (rs - 6) * 8;
if (rs == re) /* lg %rs,off(%r15) */ @@ -470,8 +468,7 @@ static int get_end(u16 seen_regs, int start) * Save and restore clobbered registers (6-15) on stack. * We save/restore registers in chunks with gap >= 2 registers. */ -static void save_restore_regs(struct bpf_jit *jit, int op, u32 stack_depth, - u16 extra_regs) +static void save_restore_regs(struct bpf_jit *jit, int op, u16 extra_regs) { u16 seen_regs = jit->seen_regs | extra_regs; const int last = 15, save_restore_size = 6; @@ -494,7 +491,7 @@ static void save_restore_regs(struct bpf_jit *jit, int op, u32 stack_depth, if (op == REGS_SAVE) save_regs(jit, rs, re); else - restore_regs(jit, rs, re, stack_depth); + restore_regs(jit, rs, re); re++; } while (re <= last); } @@ -561,8 +558,7 @@ static void bpf_jit_plt(struct bpf_plt *plt, void *ret, void *target) * Save registers and create stack frame if necessary. * See stack frame layout description in "bpf_jit.h"! */ -static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp, - u32 stack_depth) +static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp) { /* No-op for hotpatching */ /* brcl 0,prologue_plt */ @@ -595,7 +591,7 @@ static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp, jit->seen_regs |= NVREGS; } else { /* Save registers */ - save_restore_regs(jit, REGS_SAVE, stack_depth, + save_restore_regs(jit, REGS_SAVE, fp->aux->exception_boundary ? NVREGS : 0); } /* Setup literal pool */ @@ -617,8 +613,8 @@ static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp, 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); - /* aghi %r15,-STK_OFF */ - EMIT4_IMM(0xa70b0000, REG_15, -(STK_OFF + stack_depth)); + /* aghi %r15,-frame_off */ + EMIT4_IMM(0xa70b0000, REG_15, -jit->frame_off); /* stg %w1,152(%r15) (backchain) */ EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W1, REG_0, REG_15, 152); @@ -665,13 +661,13 @@ static void call_r1(struct bpf_jit *jit) /* * Function epilogue */ -static void bpf_jit_epilogue(struct bpf_jit *jit, u32 stack_depth) +static void bpf_jit_epilogue(struct bpf_jit *jit) { jit->exit_ip = jit->prg; /* Load exit code: lgr %r2,%b0 */ EMIT4(0xb9040000, REG_2, BPF_REG_0); /* Restore registers */ - save_restore_regs(jit, REGS_RESTORE, stack_depth, 0); + save_restore_regs(jit, REGS_RESTORE, 0); if (nospec_uses_trampoline()) { jit->r14_thunk_ip = jit->prg; /* Generate __s390_indirect_jump_r14 thunk */ @@ -862,7 +858,7 @@ static int sign_extend(struct bpf_jit *jit, int r, u8 size, u8 flags) * stack space for the large switch statement. */ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, - int i, bool extra_pass, u32 stack_depth) + int i, bool extra_pass) { struct bpf_insn *insn = &fp->insnsi[i]; s32 branch_oc_off = insn->off; @@ -1783,9 +1779,9 @@ 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),N(%r15) */ + /* mvc STK_OFF_TCCNT(4,%r15),frame_off+STK_OFF_TCCNT(%r15) */ _EMIT6(0xd203f000 | STK_OFF_TCCNT, - 0xf000 | (STK_OFF_TCCNT + STK_OFF + stack_depth)); + 0xf000 | (jit->frame_off + STK_OFF_TCCNT));
/* Sign-extend the kfunc arguments. */ if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) { @@ -1836,10 +1832,7 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, * goto out; */
- if (jit->seen & SEEN_STACK) - off = STK_OFF_TCCNT + STK_OFF + stack_depth; - else - off = STK_OFF_TCCNT; + off = jit->frame_off + STK_OFF_TCCNT; /* lhi %w0,1 */ EMIT4_IMM(0xa7080000, REG_W0, 1); /* laal %w1,%w0,off(%r15) */ @@ -1869,7 +1862,7 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, /* * Restore registers before calling function */ - save_restore_regs(jit, REGS_RESTORE, stack_depth, 0); + save_restore_regs(jit, REGS_RESTORE, 0);
/* * goto *(prog->bpf_func + tail_call_start); @@ -2161,7 +2154,7 @@ static int bpf_set_addr(struct bpf_jit *jit, int i) * Compile eBPF program into s390x code */ static int bpf_jit_prog(struct bpf_jit *jit, struct bpf_prog *fp, - bool extra_pass, u32 stack_depth) + bool extra_pass) { int i, insn_count, lit32_size, lit64_size; u64 kern_arena; @@ -2170,24 +2163,28 @@ static int bpf_jit_prog(struct bpf_jit *jit, struct bpf_prog *fp, jit->lit64 = jit->lit64_start; 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); + else + jit->frame_off = 0;
kern_arena = bpf_arena_get_kern_vm_start(fp->aux->arena); if (kern_arena) jit->kern_arena = _EMIT_CONST_U64(kern_arena); jit->user_arena = bpf_arena_get_user_vm_start(fp->aux->arena);
- bpf_jit_prologue(jit, fp, stack_depth); + bpf_jit_prologue(jit, fp); if (bpf_set_addr(jit, 0) < 0) return -1; for (i = 0; i < fp->len; i += insn_count) { - insn_count = bpf_jit_insn(jit, fp, i, extra_pass, stack_depth); + insn_count = bpf_jit_insn(jit, fp, i, extra_pass); if (insn_count < 0) return -1; /* Next instruction address */ if (bpf_set_addr(jit, i + insn_count) < 0) return -1; } - bpf_jit_epilogue(jit, stack_depth); + bpf_jit_epilogue(jit);
lit32_size = jit->lit32 - jit->lit32_start; lit64_size = jit->lit64 - jit->lit64_start; @@ -2263,7 +2260,6 @@ static struct bpf_binary_header *bpf_jit_alloc(struct bpf_jit *jit, */ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) { - u32 stack_depth = round_up(fp->aux->stack_depth, 8); struct bpf_prog *tmp, *orig_fp = fp; struct bpf_binary_header *header; struct s390_jit_data *jit_data; @@ -2316,7 +2312,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) * - 3: Calculate program size and addrs array */ for (pass = 1; pass <= 3; pass++) { - if (bpf_jit_prog(&jit, fp, extra_pass, stack_depth)) { + if (bpf_jit_prog(&jit, fp, extra_pass)) { fp = orig_fp; goto free_addrs; } @@ -2330,7 +2326,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp) goto free_addrs; } skip_init_ctx: - if (bpf_jit_prog(&jit, fp, extra_pass, stack_depth)) { + if (bpf_jit_prog(&jit, fp, extra_pass)) { bpf_jit_binary_free(header); fp = orig_fp; goto free_addrs;
commit e26d523edf2a62b142d2dd2dd9b87f61ed92f33a upstream.
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 --- arch/s390/net/bpf_jit.h | 55 ---------------------------- arch/s390/net/bpf_jit_comp.c | 69 ++++++++++++++++++++++++------------ 2 files changed, 47 insertions(+), 77 deletions(-) delete mode 100644 arch/s390/net/bpf_jit.h
diff --git a/arch/s390/net/bpf_jit.h b/arch/s390/net/bpf_jit.h deleted file mode 100644 index 7822ea92e54af..0000000000000 --- 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 12fda05aadf61..7907c3f9b59ab 100644 --- 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 */ @@ -56,7 +55,7 @@ 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 */ @@ -404,12 +403,26 @@ 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) */ @@ -424,7 +437,7 @@ 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) */ @@ -556,10 +569,12 @@ 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); @@ -567,8 +582,9 @@ 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. @@ -611,13 +627,15 @@ 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)); } }
@@ -1779,9 +1797,10 @@ 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) { @@ -1832,7 +1851,8 @@ 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) */ @@ -2164,7 +2184,9 @@ 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;
@@ -2647,9 +2669,10 @@ 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, @@ -2786,8 +2809,9 @@ 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() */ @@ -2844,8 +2868,9 @@ 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);
commit c861a6b147137d10b5ff88a2c492ba376cd1b8b0 upstream.
The tailcall_bpf2bpf_hierarchy_1 test hangs on s390. Its call graph is as follows:
entry() subprog_tail() bpf_tail_call_static(0) -> entry + tail_call_start subprog_tail() bpf_tail_call_static(0) -> entry + tail_call_start
entry() copies its tail call counter to the subprog_tail()'s frame, which then increments it. However, the incremented result is discarded, leading to an astronomically large number of tail calls.
Fix by writing the incremented counter back to the entry()'s frame.
Fixes: dd691e847d28 ("s390/bpf: Implement bpf_jit_supports_subprog_tailcalls()") Signed-off-by: Ilya Leoshkevich iii@linux.ibm.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20250813121016.163375-3-iii@linux.ibm.com --- arch/s390/net/bpf_jit_comp.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c index 7907c3f9b59ab..2526a3d53fadb 100644 --- a/arch/s390/net/bpf_jit_comp.c +++ b/arch/s390/net/bpf_jit_comp.c @@ -1789,13 +1789,6 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, jit->seen |= SEEN_FUNC; /* * Copy the tail call counter to where the callee expects it. - * - * Note 1: The callee can increment the tail call counter, but - * we do not load it back, since the x86 JIT does not do this - * either. - * - * Note 2: We assume that the verifier does not let us call the - * main program, which clears the tail call counter on entry. */ /* mvc tail_call_cnt(4,%r15),frame_off+tail_call_cnt(%r15) */ _EMIT6(0xd203f000 | offsetof(struct prog_frame, tail_call_cnt), @@ -1822,6 +1815,22 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, call_r1(jit); /* lgr %b0,%r2: load return value into %b0 */ EMIT4(0xb9040000, BPF_REG_0, REG_2); + + /* + * Copy the potentially updated tail call counter back. + */ + + if (insn->src_reg == BPF_PSEUDO_CALL) + /* + * mvc frame_off+tail_call_cnt(%r15), + * tail_call_cnt(4,%r15) + */ + _EMIT6(0xd203f000 | (jit->frame_off + + offsetof(struct prog_frame, + tail_call_cnt)), + 0xf000 | offsetof(struct prog_frame, + tail_call_cnt)); + break; } case BPF_JMP | BPF_TAIL_CALL: {
commit bc3905a71f02511607d3ccf732360580209cac4c upstream.
The tailcall_bpf2bpf_hierarchy_fentry test hangs on s390. Its call graph is as follows:
entry() subprog_tail() trampoline() fentry() the rest of subprog_tail() # via BPF_TRAMP_F_CALL_ORIG return to entry()
The problem is that the rest of subprog_tail() increments the tail call counter, but the trampoline discards the incremented value. This results in an astronomically large number of tail calls.
Fix by making the trampoline write the incremented tail call counter back.
Fixes: 528eb2cb87bc ("s390/bpf: Implement arch_prepare_bpf_trampoline()") Signed-off-by: Ilya Leoshkevich iii@linux.ibm.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20250813121016.163375-4-iii@linux.ibm.com --- arch/s390/net/bpf_jit_comp.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c index 2526a3d53fadb..f305cb42070df 100644 --- a/arch/s390/net/bpf_jit_comp.c +++ b/arch/s390/net/bpf_jit_comp.c @@ -2828,6 +2828,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, /* stg %r2,retval_off(%r15) */ EMIT6_DISP_LH(0xe3000000, 0x0024, REG_2, REG_0, REG_15, tjit->retval_off); + /* mvc tccnt_off(%r15),tail_call_cnt(4,%r15) */ + _EMIT6(0xd203f000 | tjit->tccnt_off, + 0xf000 | offsetof(struct prog_frame, tail_call_cnt));
im->ip_after_call = jit->prg_buf + jit->prg;
linux-stable-mirror@lists.linaro.org
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Ilya Leoshkevich