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Thu, 9 Jan 2025 03:01:37 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface MIME-Version: 1.0 Date: Thu, 09 Jan 2025 09:01:16 +0100 From: "Arnd Bergmann" To: "John Paul Adrian Glaubitz" , "Richard Henderson" , "Matt Turner" , "Eric W. Biederman" , "Kees Cook" , "Paul E. McKenney" , linux-alpha@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: "Michael Cree" , "Sam James" , "Maciej W. Rozycki" , "Geert Uytterhoeven" , "Michael Karcher" , "Chris Hofstaedtler" , util-linux@vger.kernel.org Message-Id: <24f03227-1b55-4e50-b6e9-7ac74fda2602@app.fastmail.com> In-Reply-To: <20250103140148.370368-1-glaubitz@physik.fu-berlin.de> References: <20250103140148.370368-1-glaubitz@physik.fu-berlin.de> Subject: Re: [PATCH] alpha: Fix personality flag propagation across an exec Content-Type: text/plain Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 40BFC10000A X-Stat-Signature: 8tjbfyhpeu3gjx6qdbsxicpygssj17jg X-Rspam-User: X-HE-Tag: 1736409700-390578 X-HE-Meta: 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 CC5slHZQ wHLiOnUxAFNsrvm5cvcYobN5x24QcxQP13xRJPqKKZp+eeNHqUONZN+914IMUzaijCghf9rZWS/5ARxhmOjz+KRh0yI0R5kdVYtICG7Ix8ANqOOvgxaamKmliC8HuZfCxs71NNKVKq8VKHvmZv9s+VsrfZE7L/X/Tq49yxKETPmc8Ah+ypGNpfJoOzw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jan 3, 2025, at 15:01, John Paul Adrian Glaubitz wrote: > > #define SET_PERSONALITY(EX) \ > - set_personality(((EX).e_flags & EF_ALPHA_32BIT) \ > - ? PER_LINUX_32BIT : PER_LINUX) > + set_personality((((EX).e_flags & EF_ALPHA_32BIT) \ > + ? PER_LINUX_32BIT : PER_LINUX) | (current->personality & (~PER_MASK))) This looks wrong to me: since ADDR_LIMIT_32BIT is not part of PER_MASK, executing a regular binary from a taso binary no longer reverts back to the entire 64-bit address space. It seems that the behavior on most other architectures changed in 2012 commit 16f3e95b3209 ("cross-arch: don't corrupt personality flags upon exec()"). At the time, the same bug existed on mips, parisc and tile, but those got fixed quickly. There are two related bits I don't quite understand: - Do we still care about EF_ALPHA_32BIT? I see that it gets set by "alpha-linux-ld.bfd --taso", but could not find any documentation on what that flag is actually good for. On all other architectures, the address space limit gets enforced through a per-thread setting like TIF_32BIT, not through the personality that gets inherited by the child processes. - all architectures other than x86 mask out the lower byte. Why not that one? Arnd