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Date: Tue, 6 Feb 2024 14:04:32 -0800 Message-Id: <20240206220441.38311-8-alexei.starovoitov@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-145) In-Reply-To: <20240206220441.38311-1-alexei.starovoitov@gmail.com> References: <20240206220441.38311-1-alexei.starovoitov@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net From: Alexei Starovoitov LLVM generates bpf_cast_kern and bpf_cast_user instructions while translating pointers with __attribute__((address_space(1))). rX = cast_kern(rY) is processed by the verifier and converted to normal 32-bit move: wX = wY bpf_cast_user has to be converted by JIT. rX = cast_user(rY) is aux_reg = upper_32_bits of arena->user_vm_start aux_reg <<= 32 wX = wY // clear upper 32 bits of dst register if (wX) // if not zero add upper bits of user_vm_start wX |= aux_reg JIT can do it more efficiently: mov dst_reg32, src_reg32 // 32-bit move shl dst_reg, 32 or dst_reg, user_vm_start rol dst_reg, 32 xor r11, r11 test dst_reg32, dst_reg32 // check if lower 32-bit are zero cmove r11, dst_reg // if so, set dst_reg to zero // Intel swapped src/dst register encoding in CMOVcc Signed-off-by: Alexei Starovoitov --- arch/x86/net/bpf_jit_comp.c | 41 ++++++++++++++++++++++++++++++++++++- include/linux/filter.h | 1 + kernel/bpf/core.c | 5 +++++ 3 files changed, 46 insertions(+), 1 deletion(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 883b7f604b9a..a042ed57af7b 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1272,13 +1272,14 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image bool tail_call_seen = false; bool seen_exit = false; u8 temp[BPF_MAX_INSN_SIZE + BPF_INSN_SAFETY]; - u64 arena_vm_start; + u64 arena_vm_start, user_vm_start; int i, excnt = 0; int ilen, proglen = 0; u8 *prog = temp; int err; arena_vm_start = bpf_arena_get_kern_vm_start(bpf_prog->aux->arena); + user_vm_start = bpf_arena_get_user_vm_start(bpf_prog->aux->arena); detect_reg_usage(insn, insn_cnt, callee_regs_used, &tail_call_seen); @@ -1346,6 +1347,39 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image break; case BPF_ALU64 | BPF_MOV | BPF_X: + if (insn->off == BPF_ARENA_CAST_USER) { + if (dst_reg != src_reg) + /* 32-bit mov */ + emit_mov_reg(&prog, false, dst_reg, src_reg); + /* shl dst_reg, 32 */ + maybe_emit_1mod(&prog, dst_reg, true); + EMIT3(0xC1, add_1reg(0xE0, dst_reg), 32); + + /* or dst_reg, user_vm_start */ + maybe_emit_1mod(&prog, dst_reg, true); + if (is_axreg(dst_reg)) + EMIT1_off32(0x0D, user_vm_start >> 32); + else + EMIT2_off32(0x81, add_1reg(0xC8, dst_reg), user_vm_start >> 32); + + /* rol dst_reg, 32 */ + maybe_emit_1mod(&prog, dst_reg, true); + EMIT3(0xC1, add_1reg(0xC0, dst_reg), 32); + + /* xor r11, r11 */ + EMIT3(0x4D, 0x31, 0xDB); + + /* test dst_reg32, dst_reg32; check if lower 32-bit are zero */ + maybe_emit_mod(&prog, dst_reg, dst_reg, false); + EMIT2(0x85, add_2reg(0xC0, dst_reg, dst_reg)); + + /* cmove r11, dst_reg; if so, set dst_reg to zero */ + /* WARNING: Intel swapped src/dst register encoding in CMOVcc !!! */ + maybe_emit_mod(&prog, AUX_REG, dst_reg, true); + EMIT3(0x0F, 0x44, add_2reg(0xC0, AUX_REG, dst_reg)); + break; + } + fallthrough; case BPF_ALU | BPF_MOV | BPF_X: if (insn->off == 0) emit_mov_reg(&prog, @@ -3424,6 +3458,11 @@ void bpf_arch_poke_desc_update(struct bpf_jit_poke_descriptor *poke, } } +bool bpf_jit_supports_arena(void) +{ + return true; +} + bool bpf_jit_supports_ptr_xchg(void) { return true; diff --git a/include/linux/filter.h b/include/linux/filter.h index cd76d43412d0..78ea63002531 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -959,6 +959,7 @@ bool bpf_jit_supports_kfunc_call(void); bool bpf_jit_supports_far_kfunc_call(void); bool bpf_jit_supports_exceptions(void); bool bpf_jit_supports_ptr_xchg(void); +bool bpf_jit_supports_arena(void); void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie); bool bpf_helper_changes_pkt_data(void *func); diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 2539d9bfe369..2829077f0461 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -2926,6 +2926,11 @@ bool __weak bpf_jit_supports_far_kfunc_call(void) return false; } +bool __weak bpf_jit_supports_arena(void) +{ + return false; +} + /* Return TRUE if the JIT backend satisfies the following two conditions: * 1) JIT backend supports atomic_xchg() on pointer-sized words. * 2) Under the specific arch, the implementation of xchg() is the same