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Date: Mon, 16 Mar 2020 18:54:50 +0100 From: Borislav Petkov <bp@...en8.de> To: Peter Zijlstra <peterz@...radead.org>, Jakub Jelinek <jakub@...hat.com> Cc: Sergei Trofimovich <slyfox@...too.org>, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, x86@...nel.org Subject: Re: [PATCH] x86: fix early boot crash on gcc-10 On Mon, Mar 16, 2020 at 02:42:34PM +0100, Peter Zijlstra wrote: > Right I know, I looked for it recently :/ But since this is new in 10 > and 10 isn't released yet, I figured someone can add the attribute > before it does get released. Yes, that would be a good solution. I looked at what happens briefly after building gcc10 from git and IINM, the function in question - start_secondary() - already gets the stack canary asm glue added so it checks for a stack canary. However, the stack canary value itself gets set later in that same function: /* to prevent fake stack check failure in clock setup */ boot_init_stack_canary(); so the asm glue which checks for it would need to reload the newly computed canary value (it is 0 before we compute it and thus the mismatch). So having a way to state "do not add stack canary checking to this particular function" would be optimal. And since you already have the "stack_protect" function attribute I figure adding a "no_stack_protect" one should be easy... > > Or of course you could add noinline attribute to whatever got inlined > > and contains some array or addressable variable that whatever > > -fstack-protector* mode kernel uses triggers it. With -fstack-protector-all > > it would never work even in the past I believe. > > I don't think the kernel supports -fstack-protector-all, but I could be > mistaken. The other thing I was thinking was to carve out only that function into a separate compilation unit and disable stack protector only for it. All IMHO of course. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
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