Re: arm64: copy_from_user access the last page of ddr has problem on 4.14 kernel

Will Deacon
2019-01-20T02:08:50Z

On Thu, Jan 17, 2019 at 09:57:17AM +0800, Kassey wrote:
> hi, Will
> it is hard to try on v5.0-rc2 kernel, since there is much port
> job to be done.
> dst kernel buffer is looks overwriten by some same(fix) patter
> start with "mmap" (0x6d6d7061) see below code (data from vmalloc),
> and file is mmaped (include the last phy page of ddr.)
> see below pattern and pieces of code.

Weird!

> not sure if there is boundary issue for copy_from_user, please
> help to suggest if you got some idea from the pattern, thanks.

copy_from_user() doesn't care about the physical address, so I can't see why
it would matter (assuming we haven't done something nuts elsewhere, like
double-allocate the page).

The corruption you have is reasonably regular:

> 0079c00 6d6d 7061 0000 0000 0848 fd8f 0001 0000
> 0079c10 0048 fd8f 0001 0000 0001 0000 0003 0000
> 0079c20 2000 fd83 0001 0000 1fff fd86 0001 0000
> 0079c30 0000 0000 0000 0000 700f 0000 0000 0000

Here's "mmap" again, but the record is twice as long:

> 0079c40 6d6d 7061 0000 0000 f448 ffff 0001 0000
> 0079c50 f748 ffff 0001 0000 0001 0000 0004 0000
> 0079c60 3000 fd8c 0001 0000 2fff fd8e 0001 0000
> 0079c70 0000 0000 0000 0000 700f 0000 0000 0000
> 0079c80 c103 0606 0100 be00 1009 3b00 3b07 0607
> 0079c90 0100 5700 1006 e800 8c03 3103 0100 0a00
> 0079ca0 0000 cf00 bf08 0a00 0100 5700 1006 3700
> 0079cb0 3906 0606 0100 1600 0004 4700 9902 0207

And then the whole structure repeats:

> 0079cc0 6d6d 7061 0000 0000 f808 ffff 0001 0000
> 0079cd0 f1c8 ffff 0001 0000 0001 0000 0005 0000
> 0079ce0 d000 fff8 0001 0000 efff fffa 0001 0000
> 0079cf0 0000 0000 0000 0000 700f 0000 0000 0000

> 0079d00 6d6d 7061 0000 0000 f1c8 ffff 0001 0000
> 0079d10 f388 ffff 0001 0000 0001 0000 0003 0000
> 0079d20 c000 ffdf 0001 0000 6fff fff8 0001 0000
> 0079d30 0000 0000 0000 0000 700f 0000 0000 0000
> 0079d40 9407 0901 0100 5300 0204 b400 d503 0a04
> 0079d50 0100 0000 0001 0200 7309 0202 0100 0200
> 0079d60 5000 0200 7309 0202 0400 ff00 f7ff 94ff
> 0079d70 b400 0208 0100 dc00 0000 b400 5803 0607
> 0079d80 6d6d 7061 0000 0000 f7c8 ffff 0001 0000

Do you have any applications running with the name "mmap"?

Also, have you booted with "memtest" on the command-line, so that we can
rule out any dram aliasing issues and the like?