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Date: Fri, 21 Sep 2018 11:56:41 -0700
From: Kees Cook <keescook@...omium.org>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Daniel Borkmann <daniel@...earbox.net>, Jann Horn <jannh@...gle.com>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Kristen Carlson Accardi <kristen@...ux.intel.com>, Dave Hansen <dave.hansen@...el.com>,
Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH v6 3/4] vmalloc: Add debugfs modfraginfo
On Thu, Sep 13, 2018 at 2:31 PM, Rick Edgecombe
<rick.p.edgecombe@...el.com> wrote:
> Add debugfs file "modfraginfo" for providing info on module space fragmentation.
> This can be used for determining if loadable module randomization is causing any
> problems for extreme module loading situations, like huge numbers of modules or
> extremely large modules.
>
> Sample output when KASLR is enabled and X86_64 is configured:
> Largest free space: 897912 kB
> Total free space: 1025424 kB
> Allocations in backup area: 0
>
> Sample output when just X86_64:
> Largest free space: 897912 kB
> Total free space: 1025424 kB
>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
I like having these statistics available!
> ---
> mm/vmalloc.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 101 insertions(+), 1 deletion(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 1954458..a44b902 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -18,6 +18,7 @@
> #include <linux/interrupt.h>
> #include <linux/proc_fs.h>
> #include <linux/seq_file.h>
> +#include <linux/debugfs.h>
> #include <linux/debugobjects.h>
> #include <linux/kallsyms.h>
> #include <linux/list.h>
> @@ -33,6 +34,7 @@
> #include <linux/bitops.h>
>
> #include <linux/uaccess.h>
> +#include <asm/setup.h>
> #include <asm/tlbflush.h>
> #include <asm/shmparam.h>
>
> @@ -2919,7 +2921,105 @@ static int __init proc_vmalloc_init(void)
> proc_create_seq("vmallocinfo", 0400, NULL, &vmalloc_op);
> return 0;
> }
> -module_init(proc_vmalloc_init);
> +#else
> +static int __init proc_vmalloc_init(void)
> +{
> + return 0;
> +}
> +#endif
> +
> +#if defined(CONFIG_RANDOMIZE_BASE) && defined(CONFIG_X86_64)
> +static inline unsigned long is_in_backup(unsigned long addr)
> +{
> + return addr >= MODULES_VADDR + MODULES_RAND_LEN;
> +}
> +#else
> +static inline unsigned long is_in_backup(unsigned long addr)
> +{
> + return 0;
> +}
>
> +inline bool kaslr_enabled(void);
> #endif
>
> +
> +#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_X86_64)
> +static int modulefraginfo_debug_show(struct seq_file *m, void *v)
> +{
> + unsigned long last_end = MODULES_VADDR;
> + unsigned long total_free = 0;
> + unsigned long largest_free = 0;
> + unsigned long backup_cnt = 0;
> + unsigned long gap;
> + struct vmap_area *prev, *cur = NULL;
> +
> + spin_lock(&vmap_area_lock);
> +
> + if (!pvm_find_next_prev(MODULES_VADDR, &cur, &prev) || !cur)
> + goto done;
> +
> + for (; cur->va_end <= MODULES_END; cur = list_next_entry(cur, list)) {
> + /* Don't count areas that are marked to be lazily freed */
> + if (!(cur->flags & VM_LAZY_FREE)) {
> + backup_cnt += is_in_backup(cur->va_start);
> + gap = cur->va_start - last_end;
> + if (gap > largest_free)
> + largest_free = gap;
> + total_free += gap;
> + last_end = cur->va_end;
> + }
> +
> + if (list_is_last(&cur->list, &vmap_area_list))
> + break;
> + }
> +
> +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?
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:
Reviewed-by: Kees Cook <keescook@...omium.org>
-Kees
--
Kees Cook
Pixel Security
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