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Message-ID: <87bnb0vwee.fsf@rustcorp.com.au>
Date: Thu, 12 Nov 2015 11:58:25 +1030
From: Rusty Russell <rusty@...tcorp.com.au>
To: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 4/4] module: clean up RO/NX handling.
Josh Poimboeuf <jpoimboe@...hat.com> writes:
> On Tue, Nov 10, 2015 at 12:27:34PM +1030, Rusty Russell wrote:
>> Josh Poimboeuf <jpoimboe@...hat.com> writes:
>> > On Mon, Nov 09, 2015 at 02:53:57PM +1030, Rusty Russell wrote:
>> >
>> >> @@ -1858,74 +1849,75 @@ static void mod_sysfs_teardown(struct module *mod)
>> >> /*
>> >> * LKM RO/NX protection: protect module's text/ro-data
>> >> * from modification and any data from execution.
>> >> + *
>> >> + * General layout of module is:
>> >> + * [text] [read-only-data] [writable data]
>> >> + * text_size -----^ ^ ^
>> >> + * ro_size ------------------------| |
>> >> + * size -------------------------------------------|
>> >> + *
>> >> + * These values are always page-aligned (as is base)
>> >> */
>> >> -void set_page_attributes(void *start, void *end, int (*set)(unsigned long start, int num_pages))
>> >> +static void frob_text(const struct module_layout *layout,
>> >> + int (*set_memory)(unsigned long start, int num_pages))
>> >> {
>> >> - unsigned long begin_pfn = PFN_DOWN((unsigned long)start);
>> >> - unsigned long end_pfn = PFN_DOWN((unsigned long)end);
>> >> -
>> >> - if (end_pfn > begin_pfn)
>> >> - set(begin_pfn << PAGE_SHIFT, end_pfn - begin_pfn);
>> >> + BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
>> >> + BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1));
>> >> + set_memory((unsigned long)layout->base,
>> >> + layout->text_size >> PAGE_SHIFT);
>> >
>> > Should the set_memory() call be skipped if text_size is 0?
>>
>> Not AFAICT. And in practice:
>> 1) Every module on my system has a .text section.
>> 2) Every module has a rodata section (.modinfo)
>> 3) Every module on my system has a .data section.
>>
>> So I think it would be a premature optimization.
>
> However, the frob functions are also used for init sections.
>
> A search on my Fedora system's modules for .init.* sections shows that
> most modules don't have .init.rodata and .init.data, and some modules
> don't even have .init.text.
Good point! OK, let's do some trivial benchmarking...
diff --git a/kernel/module.c b/kernel/module.c
index 77212128f34a..94ea51a20958 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1906,10 +1906,19 @@ void module_enable_ro(const struct module *mod)
static void module_enable_nx(const struct module *mod)
{
+ size_t i;
+ ktime_t start, end;
frob_rodata(&mod->core_layout, set_memory_nx);
frob_writable_data(&mod->core_layout, set_memory_nx);
- frob_rodata(&mod->init_layout, set_memory_nx);
- frob_writable_data(&mod->init_layout, set_memory_nx);
+
+ start = ktime_get_boottime();
+ for (i = 0; i < 1000000; i++) {
+ frob_rodata(&mod->init_layout, set_memory_nx);
+ frob_writable_data(&mod->init_layout, set_memory_nx);
+ }
+ end = ktime_get_boottime();
+ printk("%s init time (ns): %lu\n", module_name(mod),
+ ktime_to_ns(ktime_sub(end, start)));
}
static void module_disable_nx(const struct module *mod)
[ 2.794462] parport init time (ns): 15277714
[ 2.855277] lp init time (ns): 15207768
[ 2.909701] mac_hid init time (ns): 15409571
[ 2.975350] tpm_tis init time (ns): 15118394
[ 3.062865] parport_pc init time (ns): 15646948
[ 3.247979] virtio_balloon init time (ns): 15555578
[ 3.291373] virtio_net init time (ns): 15236362
[ 3.391361] serio_raw init time (ns): 15395063
Range & mean: 15118394-15646948(1.53559e+07+/-1.7e+05)
With a zero-check:
[ 2.530933] parport init time (ns): 12133350
[ 2.587167] lp init time (ns): 12059255
[ 2.642342] mac_hid init time (ns): 12849836
[ 2.698726] tpm_tis init time (ns): 12008736
[ 2.768969] parport_pc init time (ns): 12057191
[ 2.943308] virtio_net init time (ns): 12048224
[ 2.989983] virtio_balloon init time (ns): 12077151
[ 3.061752] serio_raw init time (ns): 12396804
Range & mean: 12008736-12849836(1.22038e+07+/-2.7e+05)
So, we did save 3ns, but it was 12ns even to call them to do nothing.
We'd save more by removing the BUG_ON checks I suspect...
Cheers,
Rusty.
diff --git a/kernel/module.c b/kernel/module.c
index 77212128f34a..9ac8952a0a72 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1863,8 +1863,9 @@ static void frob_text(const struct module_layout *layout,
{
BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1));
- set_memory((unsigned long)layout->base,
- layout->text_size >> PAGE_SHIFT);
+ if (layout->text_size)
+ set_memory((unsigned long)layout->base,
+ layout->text_size >> PAGE_SHIFT);
}
static void frob_rodata(const struct module_layout *layout,
@@ -1873,8 +1874,9 @@ static void frob_rodata(const struct module_layout *layout,
BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
- set_memory((unsigned long)layout->base + layout->text_size,
- (layout->ro_size - layout->text_size) >> PAGE_SHIFT);
+ if (layout->ro_size != layout->text_size)
+ set_memory((unsigned long)layout->base + layout->text_size,
+ (layout->ro_size - layout->text_size) >> PAGE_SHIFT);
}
static void frob_writable_data(const struct module_layout *layout,
@@ -1883,8 +1885,9 @@ static void frob_writable_data(const struct module_layout *layout,
BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1));
BUG_ON((unsigned long)layout->size & (PAGE_SIZE-1));
- set_memory((unsigned long)layout->base + layout->ro_size,
- (layout->size - layout->ro_size) >> PAGE_SHIFT);
+ if (layout->size != layout->ro_size)
+ set_memory((unsigned long)layout->base + layout->ro_size,
+ (layout->size - layout->ro_size) >> PAGE_SHIFT);
}
/* livepatching wants to disable read-only so it can frob module. */
--
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