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[176.36.0.241]) by smtp.gmail.com with ESMTPSA id mb8-20020a170906eb0800b00a1de512fa1fsm10832774ejb.186.2023.12.15.08.22.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 Dec 2023 08:22:47 -0800 (PST) Message-ID: <149715b52bdd9ec9453a8a817d8339bd1a86a4f7.camel@gmail.com> Subject: Re: [Bug Report] bpf: incorrectly pruning runtime execution path From: Eduard Zingerman To: Andrii Nakryiko Cc: Alexei Starovoitov , Hao Sun , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , bpf , Linux Kernel Mailing List Date: Fri, 15 Dec 2023 18:22:45 +0200 In-Reply-To: References: <480a5cfefc23446f7c82c5b87eef6306364132b9.camel@gmail.com> <917DAD9F-8697-45B8-8890-D33393F6CDF1@gmail.com> <9dee19c7d39795242c15b2f7aa56fb4a6c3ebffa.camel@gmail.com> <73d021e3f77161668aae833e478b210ed5cd2f4d.camel@gmail.com> <526d4ac8f6788d3323d29fdbad0e0e5d09a534db.camel@gmail.com> <2b49b96de9f8a1cd6d78cc5aebe7c35776cd2c19.camel@gmail.com> <66b2a6c45045c207d8452ad3b5786a9dc0082d79.camel@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 3.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2023-12-14 at 21:20 -0800, Andrii Nakryiko wrote: [...] > > > can we detect that any register link is broken and force checkpoint h= ere? > >=20 > > Should be possible. I'll try this in the morning and check veristat res= ults. {still working on this} > > By the way, I added some stats collection for find_equal_scalars() and = see > > the following results when run on ./test_progs: > > - maximal number of registers with same id per call: 3 > > - average number of registers with same id per call: 1.4 >=20 > What if we keep 8 extra bytes in jump/instruction history and encode > up to 8 linked registers/slots: >=20 > 1. 1 bit to mark whether it's a src_reg set, or dst_reg set > 2. 1 bit to mark whether it's a stack slot or register > 3. 6 bits (0..63 values) to record register or slot number >=20 > If we ever need more than 8 linked registers, we can just forcefully > some "links" by resetting some IDs? That should work as well. Probably don't need src/dst bit, as backtracker marks both as precise when processing conditional jump. You mean "just forcefully [breaking] some "links" by resetting ...", right? > BTW, is it only conditional jumps that need to record this linked > register sets? Did we previously discuss why we don't need this for > any other operation? Don't think that we discussed it. Here is my reasoning: the range transfer happens at find_equal_scalars() which is called only from check_cond_jmp_op(). I think there are no other effects IDs have for scalar values. Thus, covering conditional jumps seems sufficient.