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[192.26.29.3]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a5a179c80ffsm914408066b.115.2024.05.15.16.39.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 May 2024 16:39:40 -0700 (PDT) From: Kumar Kartikeya Dwivedi To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , Puranjay Mohan , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" Subject: [PATCH bpf-next v1 2/2] bpf, x86: Skip bounds checking for PROBE_MEM with SMAP Date: Wed, 15 May 2024 23:39:32 +0000 Message-ID: <20240515233932.3733815-3-memxor@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240515233932.3733815-1-memxor@gmail.com> References: <20240515233932.3733815-1-memxor@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2699; i=memxor@gmail.com; h=from:subject; bh=c5oTgP9QkkqMhl0mhuFCPOTyp5qmTdwIBTcPx9gqqZM=; b=owEBbQKS/ZANAwAKAUzgyIZIvxHKAcsmYgBmRUUlHVXLEcjnMz1ZjXdYJR6KEUpM7hl4PD0Iv CImrToA1vSJAjMEAAEKAB0WIQRLvip+Buz51YI8YRFM4MiGSL8RygUCZkVFJQAKCRBM4MiGSL8R yvT4D/oDA65a3kATSPCKOqlcWENl1KjrvVOZaJpHlN3n8hWF1Da+p7fpnz/j9v0sQEMgcZWUtu2 bVKKsA4CZRddxOn6wnNHxTsE5ilhBUtYjb9CgnacnndDL9EaQtqxOGEnxUAVo036zQAncpO3RkH lUlmZPL6WcEPQhjmbuNCof2g/YYLELjaOhSoh78NGcxW/nvDtdofJ/kJ9CF4yDEZlsz1h01UJpi 7ayH9wHivPIRCiZH1MbYdrZK1fGMwddbWXfTt8VJzqsfVja9gpzPK2s1Jg6LDtIi+wIS9/7fhlG ig2lwyaQpxvnnHqEiIpWnrQ5QSbzyk9cqM1hu5MXh7J1R7FZysDRoE+ZgkIZQMr+MS+l5RymCU3 bWD3jEj73iy4W5ZBNHcotRtPev41uD2QlfF/jxYi5z1SVkd42eL5h/owANQrRMhgy5euAkmQIui jAba3Qtf9JiJQXk6Z197S7kmsxoP5sKUyOflPPl8rZSkjQGJ97GQeYLBHAQqPB+wFlfk8wmrx1X ZVl4zo9xx/RjK03Lw1NI8vwCMUWS2YTkHr3l08RZjxNmGjjy/YwE+gr6WIsaVmQ6HeaPeHk9FDu wL2CmOcdjzWPddcQzLhY5Ycg2eBk63L6sZZkHYMLIK6pY3coSoQOzgwbxZu2QnoXS2VYzMp4xro ZEtEUmwfbN3l28Q== X-Developer-Key: i=memxor@gmail.com; a=openpgp; fpr=4BBE2A7E06ECF9D5823C61114CE0C88648BF11CA X-Patchwork-Delegate: bpf@iogearbox.net The previous patch changed the do_user_addr_fault page fault handler to invoke BPF's fixup routines (by searching exception tables and calling ex_handler_bpf). This would only occur when SMAP is enabled, such that any user address access from BPF programs running in kernel mode would reach this path and invoke the fixup routines. Relying on this behavior, disable any bounds checking instrumentation in the BPF JIT for x86 when X86_FEATURE_SMAP is available. All BPF programs execute with SMAP enabled, therefore when this feature is available, we can assume that SMAP will be enabled during program execution at runtime. This optimizes PROBE_MEM loads down to a normal unchecked load instruction. Any page faults for user or kernel addresses will be handled using the fixup routines, and the generation exception table entries for such load instructions. All in all, this ensures that PROBE_MEM loads will now incur no runtime overhead, and become practically free. Signed-off-by: Kumar Kartikeya Dwivedi --- arch/x86/net/bpf_jit_comp.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 5159c7a22922..f8a39189cddc 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1864,8 +1864,8 @@ st: if (is_imm8(insn->off)) case BPF_LDX | BPF_PROBE_MEMSX | BPF_W: insn_off = insn->off; - if (BPF_MODE(insn->code) == BPF_PROBE_MEM || - BPF_MODE(insn->code) == BPF_PROBE_MEMSX) { + if ((BPF_MODE(insn->code) == BPF_PROBE_MEM || + BPF_MODE(insn->code) == BPF_PROBE_MEMSX) && !cpu_feature_enabled(X86_FEATURE_SMAP)) { /* Conservatively check that src_reg + insn->off is a kernel address: * src_reg + insn->off > TASK_SIZE_MAX + PAGE_SIZE * and @@ -1912,6 +1912,9 @@ st: if (is_imm8(insn->off)) /* populate jmp_offset for JAE above to jump to start_of_ldx */ start_of_ldx = prog; end_of_jmp[-1] = start_of_ldx - end_of_jmp; + } else if ((BPF_MODE(insn->code) == BPF_PROBE_MEM || + BPF_MODE(insn->code) == BPF_PROBE_MEMSX)) { + start_of_ldx = prog; } if (BPF_MODE(insn->code) == BPF_PROBE_MEMSX || BPF_MODE(insn->code) == BPF_MEMSX) @@ -1924,9 +1927,13 @@ st: if (is_imm8(insn->off)) u8 *_insn = image + proglen + (start_of_ldx - temp); s64 delta; + if (cpu_feature_enabled(X86_FEATURE_SMAP)) + goto extable_fixup; + /* populate jmp_offset for JMP above */ start_of_ldx[-1] = prog - start_of_ldx; + extable_fixup: if (!bpf_prog->aux->extable) break;