From patchwork Thu Dec 3 16:02:39 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Brendan Jackman X-Patchwork-Id: 11949069 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 719D2C1B087 for ; Thu, 3 Dec 2020 16:05:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1537D207A9 for ; Thu, 3 Dec 2020 16:05:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731192AbgLCQEx (ORCPT ); Thu, 3 Dec 2020 11:04:53 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54886 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731190AbgLCQEx (ORCPT ); Thu, 3 Dec 2020 11:04:53 -0500 Received: from mail-qt1-x84a.google.com (mail-qt1-x84a.google.com [IPv6:2607:f8b0:4864:20::84a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6C0F1C094240 for ; Thu, 3 Dec 2020 08:03:27 -0800 (PST) Received: by mail-qt1-x84a.google.com with SMTP id t22so1906729qtq.2 for ; Thu, 03 Dec 2020 08:03:27 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:in-reply-to:message-id:mime-version:references:subject :from:to:cc; bh=1MZi03le10KPs72LGaJoCYUsGmV3rDzv2p96g6KE5Ew=; b=FYu5IkxouiPAp9VF4qKQKGNGOOqOP5k4M+P/ZychnqrzGYvRBm6iiTnKPLpDb3+puN QBYXh8ulHIfkSQOrlwty4j/w5hYeY1tGnuNDBtkpT22pTdEXQ/DMujSqdFcubR2Rt4mQ CibGHGq7VTGqCfE01aCewYEe7wQNmapgGhZpsJCdYnG6ZWrIcOEi8KasmDByVRScd4yl TYOF9vxlziFeu6oMMv1J5mt4YucPPciWtFFWBkn39/l+aLcZFhwGE2ilp/OpI9ySjCe+ PwNFuO1azOVNNPCyCrn1oNecLjJko9gO4BtlXwfzW9ZNpZxppWFHxMUvByxDk+5Ufbqx 32Dw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=1MZi03le10KPs72LGaJoCYUsGmV3rDzv2p96g6KE5Ew=; b=mIs97RoiZKhWCdoLbNvBLYPObh7nc/+HMmEAR9UoJZ81lFsyxYiOGO2+BU72JSaN4O 7LXgJfpO2JSsG2rAoNVGL2f0zsxmkBi/x96yRCOWFNSGhd0nzPNFGP6LHkfRnQMyPAeN WTYDIZ65HOryIBwrJqjUw6gf0B1TtAuy2FuVly3JjmhHFsKeoTuutVSmIAJttqOvL/mS qgx+m8rm9suk2J9NNzssxFpaZ0Fg0fQOCMSoDpmTjCu2xmoTTFcyxXIppZjF4RBBmooM iucPb1RRjzSLxPl0SKNBDLNs/j44AzI+EzACfp3vJRhTf9o6b+WtapbaVg9xo0LsDpZb Eumg== X-Gm-Message-State: AOAM532pVCYHXjrIxx40jsLIwOEhPRUlG7VgAra/jokGtbZRLNOvmoGD D8G0IqcxhOsGAD0VPZY5YOkvXuNLl3s5tlRtoPFUT0/Zqh4QV8hCJI2chnv8xCXDVH7e2e68eK1 fWkFV/MDqzWQz0jcTemvAtjys1h7v9g0Wn6kwzSE0sVwCV+aGcnzQ0phF01v0++s= X-Google-Smtp-Source: ABdhPJykAvi2lneDKa4CRJ+hIgXgHMTncVmHnWe45xoBh+GhN8w152/S4iOWvuiQJFh9WDHf4fhgVZBesYjnnA== Sender: "jackmanb via sendgmr" X-Received: from beeg.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:11db]) (user=jackmanb job=sendgmr) by 2002:a05:6214:2b4:: with SMTP id m20mr4110654qvv.34.1607011406442; Thu, 03 Dec 2020 08:03:26 -0800 (PST) Date: Thu, 3 Dec 2020 16:02:39 +0000 In-Reply-To: <20201203160245.1014867-1-jackmanb@google.com> Message-Id: <20201203160245.1014867-9-jackmanb@google.com> Mime-Version: 1.0 References: <20201203160245.1014867-1-jackmanb@google.com> X-Mailer: git-send-email 2.29.2.454.gaff20da3a2-goog Subject: [PATCH bpf-next v3 08/14] bpf: Add instructions for atomic_[cmp]xchg From: Brendan Jackman To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Yonghong Song , Daniel Borkmann , KP Singh , Florent Revest , linux-kernel@vger.kernel.org, Jann Horn , Brendan Jackman Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net This adds two atomic opcodes, both of which include the BPF_FETCH flag. XCHG without the BPF_FETCh flag would naturally encode atomic_set. This is not supported because it would be of limited value to userspace (it doesn't imply any barriers). CMPXCHG without BPF_FETCH woulud be an atomic compare-and-write. We don't have such an operation in the kernel so it isn't provided to BPF either. There are two significant design decisions made for the CMPXCHG instruction: - To solve the issue that this operation fundamentally has 3 operands, but we only have two register fields. Therefore the operand we compare against (the kernel's API calls it 'old') is hard-coded to be R0. x86 has similar design (and A64 doesn't have this problem). A potential alternative might be to encode the other operand's register number in the immediate field. - The kernel's atomic_cmpxchg returns the old value, while the C11 userspace APIs return a boolean indicating the comparison result. Which should BPF do? A64 returns the old value. x86 returns the old value in the hard-coded register (and also sets a flag). That means return-old-value is easier to JIT. Signed-off-by: Brendan Jackman Change-Id: I3f19ad867dfd08515eecf72674e6fdefe28424bb Acked-by: Yonghong Song --- arch/x86/net/bpf_jit_comp.c | 8 ++++++++ include/linux/filter.h | 20 ++++++++++++++++++++ include/uapi/linux/bpf.h | 4 +++- kernel/bpf/core.c | 20 ++++++++++++++++++++ kernel/bpf/disasm.c | 15 +++++++++++++++ kernel/bpf/verifier.c | 19 +++++++++++++++++-- tools/include/linux/filter.h | 20 ++++++++++++++++++++ tools/include/uapi/linux/bpf.h | 4 +++- 8 files changed, 106 insertions(+), 4 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 88cb09fa3bfb..7d29bc3bb4ff 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -831,6 +831,14 @@ static int emit_atomic(u8 **pprog, u8 atomic_op, /* src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */ EMIT2(0x0F, 0xC1); break; + case BPF_XCHG: + /* src_reg = atomic_xchg(*(u32/u64*)(dst_reg + off), src_reg); */ + EMIT1(0x87); + break; + case BPF_CMPXCHG: + /* r0 = atomic_cmpxchg(*(u32/u64*)(dst_reg + off), r0, src_reg); */ + EMIT2(0x0F, 0xB1); + break; default: pr_err("bpf_jit: unknown atomic opcode %02x\n", atomic_op); return -EFAULT; diff --git a/include/linux/filter.h b/include/linux/filter.h index 4e04d0fc454f..6186280715ed 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -280,6 +280,26 @@ static inline bool insn_is_zext(const struct bpf_insn *insn) .off = OFF, \ .imm = BPF_ADD | BPF_FETCH }) +/* Atomic exchange, src_reg = atomic_xchg((dst_reg + off), src_reg) */ + +#define BPF_ATOMIC_XCHG(SIZE, DST, SRC, OFF) \ + ((struct bpf_insn) { \ + .code = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC, \ + .dst_reg = DST, \ + .src_reg = SRC, \ + .off = OFF, \ + .imm = BPF_XCHG }) + +/* Atomic compare-exchange, r0 = atomic_cmpxchg((dst_reg + off), r0, src_reg) */ + +#define BPF_ATOMIC_CMPXCHG(SIZE, DST, SRC, OFF) \ + ((struct bpf_insn) { \ + .code = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC, \ + .dst_reg = DST, \ + .src_reg = SRC, \ + .off = OFF, \ + .imm = BPF_CMPXCHG }) + /* Memory store, *(uint *) (dst_reg + off16) = imm32 */ #define BPF_ST_MEM(SIZE, DST, OFF, IMM) \ diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 025e377e7229..53334530cc81 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -45,7 +45,9 @@ #define BPF_EXIT 0x90 /* function return */ /* atomic op type fields (stored in immediate) */ -#define BPF_FETCH 0x01 /* fetch previous value into src reg */ +#define BPF_XCHG (0xe0 | BPF_FETCH) /* atomic exchange */ +#define BPF_CMPXCHG (0xf0 | BPF_FETCH) /* atomic compare-and-write */ +#define BPF_FETCH 0x01 /* not an opcode on its own, used to build others */ /* Register numbers */ enum { diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 61e93eb7d363..28f960bc2e30 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1630,6 +1630,16 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack) (u32) SRC, (atomic_t *)(unsigned long) (DST + insn->off)); break; + case BPF_XCHG: + SRC = (u32) atomic_xchg( + (atomic_t *)(unsigned long) (DST + insn->off), + (u32) SRC); + break; + case BPF_CMPXCHG: + BPF_R0 = (u32) atomic_cmpxchg( + (atomic_t *)(unsigned long) (DST + insn->off), + (u32) BPF_R0, (u32) SRC); + break; default: goto default_label; } @@ -1647,6 +1657,16 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack) (u64) SRC, (atomic64_t *)(s64) (DST + insn->off)); break; + case BPF_XCHG: + SRC = (u64) atomic64_xchg( + (atomic64_t *)(u64) (DST + insn->off), + (u64) SRC); + break; + case BPF_CMPXCHG: + BPF_R0 = (u64) atomic64_cmpxchg( + (atomic64_t *)(u64) (DST + insn->off), + (u64) BPF_R0, (u64) SRC); + break; default: goto default_label; } diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c index 3ee2246a52ef..18357ea9a17d 100644 --- a/kernel/bpf/disasm.c +++ b/kernel/bpf/disasm.c @@ -167,6 +167,21 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs, BPF_SIZE(insn->code) == BPF_DW ? "64" : "", bpf_ldst_string[BPF_SIZE(insn->code) >> 3], insn->dst_reg, insn->off, insn->src_reg); + } else if (BPF_MODE(insn->code) == BPF_ATOMIC && + insn->imm == BPF_CMPXCHG) { + verbose(cbs->private_data, "(%02x) r0 = atomic%s_cmpxchg(*(%s *)(r%d %+d), r0, r%d)\n", + insn->code, + BPF_SIZE(insn->code) == BPF_DW ? "64" : "", + bpf_ldst_string[BPF_SIZE(insn->code) >> 3], + insn->dst_reg, insn->off, + insn->src_reg); + } else if (BPF_MODE(insn->code) == BPF_ATOMIC && + insn->imm == BPF_XCHG) { + verbose(cbs->private_data, "(%02x) r%d = atomic%s_xchg(*(%s *)(r%d %+d), r%d)\n", + insn->code, insn->src_reg, + BPF_SIZE(insn->code) == BPF_DW ? "64" : "", + bpf_ldst_string[BPF_SIZE(insn->code) >> 3], + insn->dst_reg, insn->off, insn->src_reg); } else { verbose(cbs->private_data, "BUG_%02x\n", insn->code); } diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a68adbcee370..ccf4315e54e7 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3601,10 +3601,13 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_insn *insn) { int err; + int load_reg; switch (insn->imm) { case BPF_ADD: case BPF_ADD | BPF_FETCH: + case BPF_XCHG: + case BPF_CMPXCHG: break; default: verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", insn->imm); @@ -3626,6 +3629,13 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i if (err) return err; + if (insn->imm == BPF_CMPXCHG) { + /* Check comparison of R0 with memory location */ + err = check_reg_arg(env, BPF_REG_0, SRC_OP); + if (err) + return err; + } + if (is_pointer_value(env, insn->src_reg)) { verbose(env, "R%d leaks addr into mem\n", insn->src_reg); return -EACCES; @@ -3656,8 +3666,13 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i if (!(insn->imm & BPF_FETCH)) return 0; - /* check and record load of old value into src reg */ - err = check_reg_arg(env, insn->src_reg, DST_OP); + if (insn->imm == BPF_CMPXCHG) + load_reg = BPF_REG_0; + else + load_reg = insn->src_reg; + + /* check and record load of old value */ + err = check_reg_arg(env, load_reg, DST_OP); if (err) return err; diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h index ac7701678e1a..ea99bd17d003 100644 --- a/tools/include/linux/filter.h +++ b/tools/include/linux/filter.h @@ -190,6 +190,26 @@ .off = OFF, \ .imm = BPF_ADD | BPF_FETCH }) +/* Atomic exchange, src_reg = atomic_xchg((dst_reg + off), src_reg) */ + +#define BPF_ATOMIC_XCHG(SIZE, DST, SRC, OFF) \ + ((struct bpf_insn) { \ + .code = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC, \ + .dst_reg = DST, \ + .src_reg = SRC, \ + .off = OFF, \ + .imm = BPF_XCHG }) + +/* Atomic compare-exchange, r0 = atomic_cmpxchg((dst_reg + off), r0, src_reg) */ + +#define BPF_ATOMIC_CMPXCHG(SIZE, DST, SRC, OFF) \ + ((struct bpf_insn) { \ + .code = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC, \ + .dst_reg = DST, \ + .src_reg = SRC, \ + .off = OFF, \ + .imm = BPF_CMPXCHG }) + /* Memory store, *(uint *) (dst_reg + off16) = imm32 */ #define BPF_ST_MEM(SIZE, DST, OFF, IMM) \ diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 025e377e7229..53334530cc81 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -45,7 +45,9 @@ #define BPF_EXIT 0x90 /* function return */ /* atomic op type fields (stored in immediate) */ -#define BPF_FETCH 0x01 /* fetch previous value into src reg */ +#define BPF_XCHG (0xe0 | BPF_FETCH) /* atomic exchange */ +#define BPF_CMPXCHG (0xf0 | BPF_FETCH) /* atomic compare-and-write */ +#define BPF_FETCH 0x01 /* not an opcode on its own, used to build others */ /* Register numbers */ enum {