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Message-ID: <20170815033834.2qbjj2of62udqyz3@smitten> Date: Mon, 14 Aug 2017 21:38:34 -0600 From: Tycho Andersen <tycho@...ker.com> To: Alexander Popov <alex.popov@...ux.com> Cc: kernel-hardening@...ts.openwall.com, keescook@...omium.org, pageexec@...email.hu, spender@...ecurity.net, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, x86@...nel.org, Andy Lutomirski <luto@...capital.net> Subject: Re: [PATCH RFC v3 1/1] gcc-plugins: Add stackleak feature erasing the kernel stack at the end of syscalls On Wed, Jul 12, 2017 at 09:17:51PM +0300, Alexander Popov wrote: > +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK > +void __used track_stack(void) > +{ > + unsigned long sp = (unsigned long)&sp; > + > + if (sp < current->thread.lowest_stack && > + sp >= (unsigned long)task_stack_page(current) + > + 2 * sizeof(unsigned long)) { > + current->thread.lowest_stack = sp; > + } > + > + if (unlikely((sp & ~(THREAD_SIZE - 1)) < (THREAD_SIZE / 16))) I think this check is wrong, the lhs should be (sp & (THREAD_SIZE - 1)). Otherwise, we just check that the upper bits of the stack are < THREAD_SIZE / 16, which they never will be. Tycho
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