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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id a17-20020aa7cf11000000b005612ac47d85sm951380edy.82.2024.02.09.09.20.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Feb 2024 09:20:16 -0800 (PST) Message-ID: Subject: Re: [PATCH v2 bpf-next 07/20] bpf: Add x86-64 JIT support for PROBE_MEM32 pseudo instructions. From: Eduard Zingerman To: Alexei Starovoitov , bpf@vger.kernel.org Cc: daniel@iogearbox.net, andrii@kernel.org, memxor@gmail.com, tj@kernel.org, brho@google.com, hannes@cmpxchg.org, lstoakes@gmail.com, akpm@linux-foundation.org, urezki@gmail.com, hch@infradead.org, linux-mm@kvack.org, kernel-team@fb.com Date: Fri, 09 Feb 2024 19:20:15 +0200 In-Reply-To: <20240209040608.98927-8-alexei.starovoitov@gmail.com> References: <20240209040608.98927-1-alexei.starovoitov@gmail.com> <20240209040608.98927-8-alexei.starovoitov@gmail.com> Autocrypt: addr=eddyz87@gmail.com; prefer-encrypt=mutual; keydata=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 nYzhLWGcczc6J71q1Dje0l5vIPaSFOgwmWD4DA+WvuxM/shH4rtWeodbv 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 t1iq+gsfnXbPz5AnS598ScZI1oP7OrPSFJkt/z4acEbOQDQs8aUqrd46PV jsdqGvKnXZxzylux29UTNby4jTlz9pNJM+wPrDRmGfchLDUmf6CffaUYCbu4FiId+9+dcTCDvxbABRy1C3OJ8QY7cxfJ+pEZW18fRJ0XCl/fiV/ecAOfB3HsqgTzAn555h0rkFgay0hAvMU/mAW/CFNSIxV397zm749ZNLA0L2dMy1AKuOqH+/B+/ImBfJMDjmdyJQ8WU/OFRuGLdqOd2oZrA1iuPIa+yUYyZkaZfz/emQwpIL1+Q4p1R/OplA4yc301AqruXXUcVDbEB+joHW3hy5FwK5t5OwTKatrSJBkydSF9zdXy98fYzGniRyRA65P0Ix/8J3BYB4edY2/w0Ip/mdYsYQljBY0A== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2024-02-08 at 20:05 -0800, Alexei Starovoitov wrote: > From: Alexei Starovoitov >=20 > Add support for [LDX | STX | ST], PROBE_MEM32, [B | H | W | DW] instructi= ons. > They are similar to PROBE_MEM instructions with the following differences= : > - PROBE_MEM has to check that the address is in the kernel range with > src_reg + insn->off >=3D TASK_SIZE_MAX + PAGE_SIZE check > - PROBE_MEM doesn't support store > - PROBE_MEM32 relies on the verifier to clear upper 32-bit in the registe= r > - PROBE_MEM32 adds 64-bit kern_vm_start address (which is stored in %r12 = in the prologue) > Due to bpf_arena constructions such %r12 + %reg + off16 access is guara= nteed > to be within arena virtual range, so no address check at run-time. > - PROBE_MEM32 allows STX and ST. If they fault the store is a nop. > When LDX faults the destination register is zeroed. >=20 > Signed-off-by: Alexei Starovoitov > --- It would be great to add support for these new probe instructions in disasm= , otherwise commands like "bpftool prog dump xlated" can't print them. I sort-of brute-force verified jit code generated for new instructions and disassembly seem to be as expected. [...] > @@ -1564,6 +1697,52 @@ st: if (is_imm8(insn->off)) > emit_stx(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->off); > break; > =20 > + case BPF_ST | BPF_PROBE_MEM32 | BPF_B: > + case BPF_ST | BPF_PROBE_MEM32 | BPF_H: > + case BPF_ST | BPF_PROBE_MEM32 | BPF_W: > + case BPF_ST | BPF_PROBE_MEM32 | BPF_DW: > + start_of_ldx =3D prog; > + emit_st_r12(&prog, BPF_SIZE(insn->code), dst_reg, insn->off, insn->im= m); > + goto populate_extable; > + > + /* LDX: dst_reg =3D *(u8*)(src_reg + r12 + off) */ > + case BPF_LDX | BPF_PROBE_MEM32 | BPF_B: > + case BPF_LDX | BPF_PROBE_MEM32 | BPF_H: > + case BPF_LDX | BPF_PROBE_MEM32 | BPF_W: > + case BPF_LDX | BPF_PROBE_MEM32 | BPF_DW: > + case BPF_STX | BPF_PROBE_MEM32 | BPF_B: > + case BPF_STX | BPF_PROBE_MEM32 | BPF_H: > + case BPF_STX | BPF_PROBE_MEM32 | BPF_W: > + case BPF_STX | BPF_PROBE_MEM32 | BPF_DW: > + start_of_ldx =3D prog; > + if (BPF_CLASS(insn->code) =3D=3D BPF_LDX) > + emit_ldx_r12(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->of= f); > + else > + emit_stx_r12(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->of= f); > +populate_extable: > + { > + struct exception_table_entry *ex; > + u8 *_insn =3D image + proglen + (start_of_ldx - temp); > + s64 delta; > + > + if (!bpf_prog->aux->extable) > + break; > + > + ex =3D &bpf_prog->aux->extable[excnt++]; Nit: this seem to mostly repeat exception logic for "BPF_LDX | BPF_MEM | BPF_B" & co, is there a way to abstract it a bit? Also note that there excnt is checked for overflow.