Messages in this thread | | | Date | Tue, 11 Jan 2022 16:18:36 +0200 | From | Andy Shevchenko <> | Subject | Re: [PATCH v1 1/1] vsprintf: Fix potential unaligned access |
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On Tue, Jan 11, 2022 at 04:13:37PM +0200, Sakari Ailus wrote: > On Tue, Jan 11, 2022 at 01:22:29PM +0200, Andy Shevchenko wrote: > > On Tue, Jan 11, 2022 at 12:54:41PM +0200, Sakari Ailus wrote: > > > On Tue, Jan 11, 2022 at 12:10:28PM +0200, Andy Shevchenko wrote: > > > > On Tue, Jan 11, 2022 at 12:12:46AM +0200, Sakari Ailus wrote: > > > > > On Mon, Jan 10, 2022 at 10:50:49PM +0200, Andy Shevchenko wrote: > > > > > > The %p4cc specifier in some cases might get an unaligned pointer. > > > > > > Due to this we need to make copy to local variable once to avoid > > > > > > potential crashes on some architectures due to improper access. > > > > > > > > > > I guess this problem exists virtually everywhere where pointers are being > > > > > handled: the pointer could be unaligned. > > > > > > > > True. And my patch improves the situation. > > > > See, for example, 0f70fe605fad ("hexdump: fix for non-aligned buffers"). > > > > > > This is different since there's no guarantee of a void pointer's alignment. > > > > > > The pixelformat used for %p4cc is a pointer to u32. > > > > Oh, look at the %p, compiler doesn't know about the %p extensions and caller > > may supply whatever they want, i.e. %p may take any address that can be kept > > in void *. Actual argument _is_ void *. What you put there as u32 is just > > personal expectation, and not the reality. > > If you assume this, you should add get_unaligned() calls in all places > where you're casting a type to another with higher alignment requirements.
Those places so far were not subject of any reports, but ideally yes, you are right (in a scope of %p extensions, otherwise it's silly).
I will leave this to the VSPRINTF / PRINTK maintainers to proceed. Personally I found this patch useful since we don't know what other user will do unaligned call to it.
-- With Best Regards, Andy Shevchenko
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