From: Abhishek Dubey <[email protected]> Move the long branch address space to the bottom of the long branch stub. This allows uninterrupted disassembly until the last 8 bytes. Exclude these last bytes from the overall program length to prevent failure in assembly generation. Also, align dummy_tramp_addr field with 8-byte boundary.
Following is disassembler output for test program with moved down dummy_tramp_addr field: ..... ..... pc:68 left:44 a6 03 08 7c : mtlr 0 pc:72 left:40 bc ff ff 4b : b .-68 pc:76 left:36 a6 02 68 7d : mflr 11 pc:80 left:32 05 00 9f 42 : bcl 20, 31, .+4 pc:84 left:28 a6 02 88 7d : mflr 12 pc:88 left:24 14 00 8c e9 : ld 12, 20(12) pc:92 left:20 a6 03 89 7d : mtctr 12 pc:96 left:16 a6 03 68 7d : mtlr 11 pc:100 left:12 20 04 80 4e : bctr pc:104 left:8 c0 34 1d 00 : Failure log: Can't disasm instruction at offset 104: c0 34 1d 00 00 00 00 c0 Disassembly logic can truncate at 104, ignoring last 8 bytes. Update the dummy_tramp_addr field offset calculation from the end of the program to reflect its new location, for bpf_arch_text_poke() to update the actual trampoline's address in this field. All BPF trampoline selftests continue to pass with this patch applied. Signed-off-by: Abhishek Dubey <[email protected]> --- arch/powerpc/net/bpf_jit_comp.c | 45 +++++++++++++++++++++++++-------- 1 file changed, 34 insertions(+), 11 deletions(-) diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index 7a78e03d482f..f8f6305b0d9f 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -51,7 +51,9 @@ asm ( void bpf_jit_build_fentry_stubs(u32 *image, struct codegen_context *ctx) { - int ool_stub_idx, long_branch_stub_idx; + int ool_stub_idx, long_branch_stub_idx, tramp_load_offset; + bool tramp_needs_align; + u32 tramp_idx; /* * Out-of-line stub: @@ -70,27 +72,45 @@ void bpf_jit_build_fentry_stubs(u32 *image, struct codegen_context *ctx) /* * Long branch stub: - * .long <dummy_tramp_addr> * mflr r11 * bcl 20,31,$+4 - * mflr r12 - * ld r12, -8-SZL(r12) + * mflr r12 // lr/r12 stores current pc + * ld r12, 20(r12) // offset(dummy_tramp_addr) from prev inst. is 20 * mtctr r12 - * mtlr r11 // needed to retain ftrace ABI + * mtlr r11 // needed to retain ftrace ABI * bctr + * nop // Optional, for mem alignment of dummy_tramp_addr + * .long <dummy_tramp_addr> */ - if (image) - *((unsigned long *)&image[ctx->idx]) = (unsigned long)dummy_tramp; - ctx->idx += SZL / 4; long_branch_stub_idx = ctx->idx; EMIT(PPC_RAW_MFLR(_R11)); EMIT(PPC_RAW_BCL4()); EMIT(PPC_RAW_MFLR(_R12)); - EMIT(PPC_RAW_LL(_R12, _R12, -8-SZL)); + + /* Relative offset of dummy_tramp_addr wrt start of long branch stub */ + tramp_idx = long_branch_stub_idx + 7; + /* + * Image layout need not be considered 8-byte aligned. + * Lower 3 bits must be clear for 8-bytes alignment. + * Adjust offset for padding NOP before dummy_tramp_addr + */ + tramp_needs_align = (((unsigned long)&image[tramp_idx]) & 7) != 0; + tramp_load_offset = tramp_needs_align ? 24 : 20; + + EMIT(PPC_RAW_LL(_R12, _R12, tramp_load_offset)); EMIT(PPC_RAW_MTCTR(_R12)); EMIT(PPC_RAW_MTLR(_R11)); EMIT(PPC_RAW_BCTR()); + /* align dummy_tramp_addr to 8 bytes */ + if (tramp_needs_align) + EMIT(PPC_RAW_NOP()); + + if (image) + *((unsigned long *)&image[ctx->idx]) = (unsigned long)dummy_tramp; + + ctx->idx += SZL / 4; + if (!bpf_jit_ool_stub) { bpf_jit_ool_stub = (ctx->idx - ool_stub_idx) * 4; bpf_jit_long_branch_stub = (ctx->idx - long_branch_stub_idx) * 4; @@ -1206,7 +1226,6 @@ static void do_isync(void *info __maybe_unused) * b bpf_func + 4 * 3. Long branch stub: * long_branch_stub: - * .long <branch_addr>/<dummy_tramp> * mflr r11 * bcl 20,31,$+4 * mflr r12 @@ -1214,6 +1233,8 @@ static void do_isync(void *info __maybe_unused) * mtctr r12 * mtlr r11 // needed to retain ftrace ABI * bctr + * nop // optinonal, mem align dummy_tramp field + * .long <branch_addr>/<dummy_tramp> * * dummy_tramp is used to reduce synchronization requirements. * @@ -1315,10 +1336,12 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type old_t, * 1. Update the address in the long branch stub: * If new_addr is out of range, we will have to use the long branch stub, so patch new_addr * here. Otherwise, revert to dummy_tramp, but only if we had patched old_addr here. + * + * dummy_tramp_addr moved to bottom of long branch stub. */ if ((new_addr && !is_offset_in_branch_range(new_addr - ip)) || (old_addr && !is_offset_in_branch_range(old_addr - ip))) - ret = patch_ulong((void *)(bpf_func_end - bpf_jit_long_branch_stub - SZL), + ret = patch_ulong((void *)(bpf_func_end - SZL), /* SZL: dummy_tramp_addr offset */ (new_addr && !is_offset_in_branch_range(new_addr - ip)) ? (unsigned long)new_addr : (unsigned long)dummy_tramp); if (ret) -- 2.52.0
