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Fri, 19 Sep 2025 12:19:10 -0700 (PDT) Received: from mail.gmail.com ([2a04:ee41:4:b2de:1ac0:4dff:fe0f:3782]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46139123102sm135097665e9.9.2025.09.19.12.19.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Sep 2025 12:19:10 -0700 (PDT) Date: Fri, 19 Sep 2025 19:25:21 +0000 From: Anton Protopopov To: Eduard Zingerman Cc: bpf@vger.kernel.org, Alexei Starovoitov , Andrii Nakryiko , Anton Protopopov , Daniel Borkmann , Quentin Monnet , Yonghong Song Subject: Re: [PATCH v3 bpf-next 07/13] bpf, x86: allow indirect jumps to r8...r15 Message-ID: References: <20250918093850.455051-1-a.s.protopopov@gmail.com> <20250918093850.455051-8-a.s.protopopov@gmail.com> <59dd1a009a5682d4b16df81e097a1a1b43308a28.camel@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On 25/09/19 11:38AM, Eduard Zingerman wrote: > On Fri, 2025-09-19 at 11:25 -0700, Eduard Zingerman wrote: > > [...] > > > > --- a/arch/x86/net/bpf_jit_comp.c > > > +++ b/arch/x86/net/bpf_jit_comp.c > > > @@ -660,24 +660,38 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t, > > > > > > #define EMIT_LFENCE() EMIT3(0x0F, 0xAE, 0xE8) > > > > > > -static void emit_indirect_jump(u8 **pprog, int reg, u8 *ip) > > > +static void __emit_indirect_jump(u8 **pprog, int reg, bool ereg) > > > { > > > u8 *prog = *pprog; > > > > > > + if (ereg) > > > + EMIT1(0x41); > > > + > > > + EMIT2(0xFF, 0xE0 + reg); > > > + > > > + *pprog = prog; > > > +} > > > + > > > +static void emit_indirect_jump(u8 **pprog, int bpf_reg, u8 *ip) > > > +{ > > [...] > > > > } else { > > > - EMIT2(0xFF, 0xE0 + reg); /* jmp *%\reg */ > > > + __emit_indirect_jump(pprog, reg, ereg); > > > > You need to re-read *pprog after __emit_indirect_jump() call > > this is what causes KASAN error I reported in the sibling thread. > > W/o re-reading it the FF E1 emitted above is overwritten to CC E1 > > by EMIT1(0xCC) below. > > > > > if (IS_ENABLED(CONFIG_MITIGATION_RETPOLINE) || IS_ENABLED(CONFIG_MITIGATION_SLS)) > > > EMIT1(0xCC); /* int3 */ > > > } > > Or just move the EMIT1(0xCC) inside __emit_indirect_jump(). > It is probably necessary to correctly do mitigations anyway, wdyt? Thanks a lot for bisecting! I think better is to re-read, as in the other branch we do not emit CC