Messages in this thread | | | Date | Mon, 5 Jan 2009 18:28:48 +0300 | From | Cyrill Gorcunov <> | Subject | Re: [PATCH] mm: __nr_to_section - make it safe against overflow |
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[Christoph Lameter - Mon, Jan 05, 2009 at 09:10:57AM -0600] | On Mon, 5 Jan 2009, Cyrill Gorcunov wrote: | | > /* | > * This is, logically, a pointer to an array of struct | > @@ -980,9 +986,12 @@ extern struct mem_section mem_section[NR | > | > static inline struct mem_section *__nr_to_section(unsigned long nr) | > { | > - if (!mem_section[SECTION_NR_TO_ROOT(nr)]) | > + unsigned long idx = SECTION_NR_TO_ROOT(nr); | > + WARN_ON_ONCE(idx >= NR_SECTION_ROOTS); | > + | > + if (idx >=NR_SECTION_ROOTS || !mem_section[idx]) | > return NULL; | > - return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK]; | > + return &mem_section[idx][nr & SECTION_ROOT_MASK]; | > } | > extern int __section_nr(struct mem_section* ms); | > extern unsigned long usemap_size(void); | | Not that you are adding code to numerous hot code path. Plus this is a | frequently used inline. Code size is going to increase if you do this.
yes, I know, that is why I've changed WARN_ON_ONCE to plain WARN_ON.
| | I would think that the code does not have the tests because of performance | and code size concerns. Can we just say that a sane nr must be passed to | __nr_section? |
If you mean did I test this patch for speed regresson then to be fair -- no, I didn't. BUT we have a number of macros wich are self protective like present_section which is used havily too. On the other hand -- bad argument passed to __nr_to_section will be (and it is now) really harmfull -- since it would allow to reference a memory outside the valid bounds. The second -- SECTION_ROOT_MASK wich is fragile, any attempt to modify mem_section structure will silently lead to insane referencing, that is why it deserve a comment on top of structure.
Don't know Christoph, if it really that important to not spend a few cycles here in a sake of safety -- we could easily drop this patch.
- Cyrill -
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