Date: Mon, 24 Sep 2018 13:03:33 -0700 From: Kees Cook <keescook@...omium.org> To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com> Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "daniel@...earbox.net" <daniel@...earbox.net>, "jannh@...gle.com" <jannh@...gle.com>, "arjan@...ux.intel.com" <arjan@...ux.intel.com>, "tglx@...utronix.de" <tglx@...utronix.de>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "x86@...nel.org" <x86@...nel.org>, "kristen@...ux.intel.com" <kristen@...ux.intel.com>, "hpa@...or.com" <hpa@...or.com>, "mingo@...hat.com" <mingo@...hat.com>, "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "Hansen, Dave" <dave.hansen@...el.com> Subject: Re: [PATCH v6 3/4] vmalloc: Add debugfs modfraginfo On Mon, Sep 24, 2018 at 11:58 AM, Edgecombe, Rick P <rick.p.edgecombe@...el.com> wrote: > On Fri, 2018-09-21 at 11:56 -0700, Kees Cook wrote: >> On Thu, Sep 13, 2018 at 2:31 PM, Rick Edgecombe >> <rick.p.edgecombe@...el.com> wrote: >> > +done: >> > + gap = (MODULES_END - last_end); >> > + if (gap > largest_free) >> > + largest_free = gap; >> > + total_free += gap; >> > + >> > + spin_unlock(&vmap_area_lock); >> > + >> > + seq_printf(m, "\tLargest free space:\t%lu kB\n", largest_free / >> > 1024); >> > + seq_printf(m, "\t Total free space:\t%lu kB\n", total_free / 1024); >> > + >> > + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && kaslr_enabled()) >> > + seq_printf(m, "Allocations in backup area:\t%lu\n", >> > backup_cnt); >> I don't think the IS_ENABLED is needed here? > The reason for this is that for ARCH=um, CONFIG_X86_64 is defined but > kaslr_enabled is not. kaslr_enabled is declared above to protect against a > compiler error. > > So IS_ENABLED(CONFIG_RANDOMIZE_BASE) is protecting kaslr_enabled from causing a > linker error. It gets constant evaluated to 0 and the compiler optimizes out the > kaslr_enabled call. Thought it was better to guard with CONFIG_RANDOMIZE_BASE > than with CONFIG_UM, to try to catch the broader situation. I guess I could move > it to a helper inside ifdefs instead. Was trying to keep the ifdef-ed code down. Ah yes, UM. Perhaps kaslr_enabled() could be defined somewhere so that it would link sanely? (Maybe in module.h?) >> I wonder if there is a better way to arrange this code that uses fewer >> ifdefs, etc. Maybe a single CONFIG that capture whether or not >> fine-grained module randomization is built in, like: >> >> config RANDOMIZE_FINE_MODULE >> def_bool y if RANDOMIZE_BASE && X86_64 >> >> #ifdef CONFIG_RANDOMIZE_FINE_MODULE >> ... >> #endif >> >> But that doesn't capture the DEBUG_FS and PROC_FS bits ... so ... >> maybe not worth it. I guess, either way: > Hmmm, didn't know about that. Would clean it up some at least. > > I wish the debugfs info could be in module.c to help with this IFDEFs, but it > needs vmalloc internals. MODULES_VADDR is not standardized across the ARCH's as > well, so this was my best attempt to implement this without having to make > changes in other architectures. Yeah, I've long wanted to try to sandardize the module+vmalloc guts, but it's just different enough in each architecture that it eludes people. -Kees -- Kees Cook Pixel Security
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