Messages in this thread | | | Date | Mon, 18 Feb 2019 16:07:27 +0800 | From | Baoquan He <> | Subject | Re: [PATCH v3 3/6] mm: Add build time sanity check for struct page size |
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On 02/17/19 at 08:50am, Kees Cook wrote: > On Sat, Feb 16, 2019 at 6:02 AM Baoquan He <bhe@redhat.com> wrote: > > > > Size of struct page might be larger than 64 bytes if debug options > > enabled, or fields added for debugging intentionally. Yet an upper > > limit need be added at build time to trigger an alert in case the > > size is too big to boot up system, warning people to check if it's > > be done on purpose in advance. > > > > Here 1/4 of PAGE_SIZE is chosen since system must have been insane > > with this value. For those systems with PAGE_SIZE larger than 4KB, > > 1KB is simply taken. > > > > Signed-off-by: Baoquan He <bhe@redhat.com> > > --- > > mm/page_alloc.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 35fdde041f5c..eb6c8e22333b 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -67,6 +67,7 @@ > > #include <linux/lockdep.h> > > #include <linux/nmi.h> > > #include <linux/psi.h> > > +#include <linux/sizes.h> > > > > #include <asm/sections.h> > > #include <asm/tlbflush.h> > > @@ -7084,6 +7085,7 @@ void __init free_area_init_nodes(unsigned long *max_zone_pfn) > > unsigned long start_pfn, end_pfn; > > int i, nid; > > > > + BUILD_BUG_ON(sizeof(struct page) > min_t(size_t, SZ_1K, PAGE_SIZE)); > > Are there systems with PAGE_SIZE < 1K? Maybe this should just be a > direct SZ_1K check?
This check was suggested by Kirill, I forgot adding his "Suggested-by", sorry abou that.
Originally he suggested to add code in generic place like this:
BUILD_BUG_ON(sizeof(struct page) < min(SZ_1K, PAGE_SIZE/4));
In later post, the kbuild test robot reported an build error on i386 ARCH,
http://lkml.kernel.org/r/20180911074733.GX1740@192.168.1.3
From the report hint, I thought 'PAGE_SIZE/4' also related to the macro expansion, so change it as min_t(size_t, SZ_1K, PAGE_SIZE).
Just now I tried the build again, changing it back to 'PAGE_SIZE/4' also works.
BUILD_BUG_ON(sizeof(struct page) > min_t(size_t, SZ_1K, PAGE_SIZE/4));
I guess Kirill wants to make it as self explanatory for this check by suggesting it as min(SZ_1K, PAGE_SIZE/4), to stress the 'PAGE_SIZE/4'. As he said in mail thread, "If struct page is more than 1/4 of PAGE_SIZE something is horribly broken".
lkml.kernel.org/r/20180903102642.rmzawwqsqjvh2mkb@kshutemo-mobl1
Just try to give more details about this adding, not defend. I am fine to take any of them.
> (Also, perhaps this should use the new static_assert where struct page > is defined?)
I searched with 'git grep', didn't find static_assert macro or function. And also no finding in include/linux/mm_types.h. Could you please be more specific?
Thanks Baoquan > > > /* Record where the zone boundaries are */ > > memset(arch_zone_lowest_possible_pfn, 0, > > sizeof(arch_zone_lowest_possible_pfn)); > > -- > > 2.17.2 > > > > > -- > Kees Cook
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