Date: Thu, 5 Jan 2017 08:40:29 -0800 From: Thomas Garnier <thgarnie@...gle.com> To: Arjan van de Ven <arjan@...ux.intel.com> Cc: Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>, Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave@...1.net>, Chen Yucong <slaoub@...il.com>, Paul Gortmaker <paul.gortmaker@...driver.com>, Andrew Morton <akpm@...ux-foundation.org>, Masahiro Yamada <yamada.masahiro@...ionext.com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Anna-Maria Gleixner <anna-maria@...utronix.de>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, Michael Ellerman <mpe@...erman.id.au>, Juergen Gross <jgross@...e.com>, Richard Weinberger <richard@....at>, "the arch/x86 maintainers" <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl> Subject: Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location On Thu, Jan 5, 2017 at 7:08 AM, Arjan van de Ven <arjan@...ux.intel.com> wrote: > On 1/5/2017 12:11 AM, Ingo Molnar wrote: >> >> >> * Thomas Garnier <thgarnie@...gle.com> wrote: >> >>> Each processor holds a GDT in its per-cpu structure. The sgdt >>> instruction gives the base address of the current GDT. This address can >>> be used to bypass KASLR memory randomization. With another bug, an >>> attacker could target other per-cpu structures or deduce the base of the >>> main memory section (PAGE_OFFSET). >>> >>> In this change, a space is reserved at the end of the memory range >>> available for KASLR memory randomization. The space is big enough to hold >>> the maximum number of CPUs (as defined by setup_max_cpus). Each GDT is >>> mapped at specific offset based on the target CPU. Note that if there is >>> not enough space available, the GDTs are not remapped. >>> >>> The document was changed to mention GDT remapping for KASLR. This patch >>> also include dump page tables support. >>> >>> This patch was tested on multiple hardware configurations and for >>> hibernation support. >> >> >>> void kernel_randomize_memory(void); >>> +void kernel_randomize_smp(void); >>> +void* kaslr_get_gdt_remap(int cpu); >> >> >> Yeah, no fundamental objections from me to the principle, but I get some >> bad vibes >> from the naming here: seeing that kernel_randomize_smp() actually makes >> things >> less random. >> > > kernel_unrandomize_smp() ... > That seems like a better name. > one request.. can we make sure this unrandomization is optional? > Well, it happens only when KASLR memory randomization is enabled. Do you think it should have a separate config option? -- Thomas
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