Re: [PATCH v2] arm64: kaslr: Fix up the kernel image alignment

[Srinivas Ramana]

On 03/22/2017 06:10 PM, Will Deacon wrote:
> On Wed, Mar 22, 2017 at 12:16:24PM +0000, Ard Biesheuvel wrote:
> > On 22 March 2017 at 11:38, Srinivas Ramana <sramana@xxxxxxxxxxxxxx> wrote:
> > > From: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
> > >
> > > If kernel image extends across alignment boundary, existing
> > > code increases the KASLR offset by size of kernel image. The
> > > offset is masked after resizing. There are cases, where after
> > > masking, we may still have kernel image extending across
> > > boundary. This eventually results in only 2MB block getting
> > > mapped while creating the page tables. This results in data aborts
> > > while accessing unmapped regions during second relocation (with
> > > kaslr offset) in __primary_switch. To fix this problem, round up the
> > > kernel image size, by swapper block size, before adding it for
> > > correction.
> > >
> > > For example consider below case, where kernel image still crosses
> > > 1GB alignment boundary, after masking the offset, which is fixed
> > > by rounding up kernel image size.
> > >
> > > SWAPPER_TABLE_SHIFT = 30
> > > Swapper using section maps with section size 2MB.
> > > CONFIG_PGTABLE_LEVELS = 3
> > > VA_BITS = 39
> > >
> > > _text  : 0xffffff8008080000
> > > _end   : 0xffffff800aa1b000
> > > offset : 0x1f35600000
> > > mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1)
> > >
> > > (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7c
> > > (_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d
> > >
> > > offset after existing correction (before mask) = 0x1f37f9b000
> > > (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d
> > > (_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d
> > >
> > > offset (after mask) = 0x1f37e00000
> > > (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7c
> > > (_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d
> > >
> > > new offset w/ rounding up = 0x1f38000000
> > > (_text + offset) >> SWAPPER_TABLE_SHIFT = 0x3fffffe7d
> > > (_end + offset) >> SWAPPER_TABLE_SHIFT  = 0x3fffffe7d
> > >
> > > Fixes: f80fb3a3d508 ("arm64: add support for kernel ASLR")
> > > Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
> > > Signed-off-by: Srinivas Ramana <sramana@xxxxxxxxxxxxxx>
> >
> > Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> >
> > ... and thanks for the excellent commit log message!
>
> Thanks both. I've picked this up as a fix.
>
> Will

Thanks Ard and Will for the review and picking this patch.
can we also CC: <stable@xxxxxxxxxxxxxxx> ?

Thanks,
-- Srinivas R


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