With PCREL addressing, there is no kernel TOC. So, it is not setup in prologue when PCREL addressing is used. But the number of instructions to skip on a tail call was not adjusted accordingly. That resulted in not so obvious failures while using tailcalls. 'tailcalls' selftest crashed the system with the below call trace:

bpf_test_run+0xe8/0x3cc (unreliable) bpf_prog_test_run_skb+0x348/0x778 __sys_bpf+0xb04/0x2b00 sys_bpf+0x28/0x38 system_call_exception+0x168/0x340 system_call_vectored_common+0x15c/0x2ec

Also, as bpf programs are always module addresses and a bpf helper in general is a core kernel text address, using PC relative addressing often fails with "out of range of pcrel address" error. Switch to using kernel base for relative addressing to handle this better.

Fixes: 7e3a68be42e1 ("powerpc/64: vmlinux support building with PCREL addresing") Cc: stable@vger.kernel.org Signed-off-by: Hari Bathini hbathini@linux.ibm.com ---

* Changes in v4: - Fix out of range errors by switching to kernelbase instead of PC for relative addressing.

* Changes in v3: - New patch to fix tailcall issues with PCREL addressing.

arch/powerpc/net/bpf_jit_comp64.c | 30 ++++++++++++++++-------------- 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c index 79f23974a320..4de08e35e284 100644 --- a/arch/powerpc/net/bpf_jit_comp64.c +++ b/arch/powerpc/net/bpf_jit_comp64.c @@ -202,7 +202,8 @@ void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx) EMIT(PPC_RAW_BLR()); }

-static int bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx, u64 func) +static int +bpf_jit_emit_func_call_hlp(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func) { unsigned long func_addr = func ? ppc_function_entry((void *)func) : 0; long reladdr; @@ -211,19 +212,20 @@ static int bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx, u return -EINVAL;

if (IS_ENABLED(CONFIG_PPC_KERNEL_PCREL)) { - reladdr = func_addr - CTX_NIA(ctx); + reladdr = func_addr - local_paca->kernelbase;

if (reladdr >= (long)SZ_8G || reladdr < -(long)SZ_8G) { - pr_err("eBPF: address of %ps out of range of pcrel address.\n", - (void *)func); + pr_err("eBPF: address of %ps out of range of 34-bit relative address.\n", + (void *)func); return -ERANGE; } - /* pla r12,addr */ - EMIT(PPC_PREFIX_MLS | __PPC_PRFX_R(1) | IMM_H18(reladdr)); - EMIT(PPC_INST_PADDI | ___PPC_RT(_R12) | IMM_L(reladdr)); - EMIT(PPC_RAW_MTCTR(_R12)); - EMIT(PPC_RAW_BCTR()); - + EMIT(PPC_RAW_LD(_R12, _R13, offsetof(struct paca_struct, kernelbase))); + /* Align for subsequent prefix instruction */ + if (!IS_ALIGNED((unsigned long)fimage + CTX_NIA(ctx), 8)) + EMIT(PPC_RAW_NOP()); + /* paddi r12,r12,addr */ + EMIT(PPC_PREFIX_MLS | __PPC_PRFX_R(0) | IMM_H18(reladdr)); + EMIT(PPC_INST_PADDI | ___PPC_RT(_R12) | ___PPC_RA(_R12) | IMM_L(reladdr)); } else { reladdr = func_addr - kernel_toc_addr(); if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) { @@ -233,9 +235,9 @@ static int bpf_jit_emit_func_call_hlp(u32 *image, struct codegen_context *ctx, u

EMIT(PPC_RAW_ADDIS(_R12, _R2, PPC_HA(reladdr))); EMIT(PPC_RAW_ADDI(_R12, _R12, PPC_LO(reladdr))); - EMIT(PPC_RAW_MTCTR(_R12)); - EMIT(PPC_RAW_BCTRL()); } + EMIT(PPC_RAW_MTCTR(_R12)); + EMIT(PPC_RAW_BCTRL());

return 0; } @@ -285,7 +287,7 @@ static int bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32 o int b2p_index = bpf_to_ppc(BPF_REG_3); int bpf_tailcall_prologue_size = 8;

- if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2)) + if (!IS_ENABLED(CONFIG_PPC_KERNEL_PCREL) && IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2)) bpf_tailcall_prologue_size += 4; /* skip past the toc load */

/* @@ -993,7 +995,7 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code return ret;

if (func_addr_fixed) - ret = bpf_jit_emit_func_call_hlp(image, ctx, func_addr); + ret = bpf_jit_emit_func_call_hlp(image, fimage, ctx, func_addr); else ret = bpf_jit_emit_func_call_rel(image, fimage, ctx, func_addr);