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J . Lu" , Yu-cheng Yu , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, libc-alpha@sourceware.org Subject: Re: [PATCH v2 2/3] arm64: Enable BTI for main executable as well as the interpreter Message-ID: <20210610153426.GP4187@arm.com> References: <20210604112450.13344-1-broonie@kernel.org> <20210604112450.13344-3-broonie@kernel.org> <20210609151713.GL4187@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210610_083532_906122_0E6F25F9 X-CRM114-Status: GOOD ( 24.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Jun 10, 2021 at 02:19:05PM +0100, Mark Brown wrote: > On Wed, Jun 09, 2021 at 04:17:13PM +0100, Dave Martin wrote: > > On Fri, Jun 04, 2021 at 12:24:49PM +0100, Mark Brown wrote: > > > > - if (system_supports_bti() && has_interp == is_interp && > > > - (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) > > > - arch->flags |= ARM64_ELF_BTI; > > > + if (system_supports_bti() && > > > + (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) { > > > + if (is_interp) { > > > + arch->flags |= ARM64_ELF_INTERP_BTI; > > > + } else { > > > + arch->flags |= ARM64_ELF_EXEC_BTI; > > > + } > > > Nit: surplus curlies? (coding-style.rst does actually say to drop them > > when all branches of an if are single-statement one-liners -- I had > > presumed I was just being pedantic...) > > I really think this hurts readability with the nested if inside > another if with a multi-line condition. So long as there is a reason rather than it being purely an accident of editing, that's fine. (Though if the nested if can be flattened so that this becomes a non- issue, that's good too :) > > > - if (prot & PROT_EXEC) > > > - prot |= PROT_BTI; > > > + if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp) > > > + prot |= PROT_BTI; > > > + } > > > Is it worth adding () around the bitwise-& expressions? I'm always a > > little uneasy about the operator precedence of binary &, although > > without looking it up I think you're correct. > > Sure. I'm fairly sure the compiler would've complained about > this case if it were ambiguous, I'm vaguely surprised it didn't > already. I was vaguely surprised too -- though I didn't try to compile this myself yet. Anyway, not a huge deal. Adding a helper to generate the appropriate mask would make this issue go away in any case, but so long as you're confident this is being evaluated as intended I can take your word for it. > > Feel free to adopt if this appeals to you, otherwise I'm also fine with > > your version.) > > I'll see what I think when I get back to looking at this > properly. Ack -- again, this was just a suggestion. I can also live with your original code if you ultimately decide to stick with that. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel