Re: [PATCH 1/3] MIPS: KASLR: Correcte valid bits in apply_r_mips_26_rel

[Jinyang He]

Hi,

On 11/19/2020 08:36 PM, Thomas Bogendoerfer wrote:
> On Thu, Nov 19, 2020 at 10:29:12AM +0800, Jinyang He wrote:
> > Apply_r_mips_26_rel() relocates instructions like j, jal and etc. These
> > instructions consist of 6bits function field and 26bits address field.
> > The value of target_addr as follows,
> > =================================================================
> > |     high 4bits           |            low 28bits              |
> > =================================================================
> > |the high 4bits of this PC | the low 26bits of instructions << 2|
> > =================================================================
> > Thus, loc_orig and log_new both need high 4bits ranther than high 6bits.
> 						  rather
>
> > Replace 0x3ffffff with 0xfffffff.
> >
> > Signed-off-by: Jinyang He <hejinyang@xxxxxxxxxxx>
> > ---
> >   arch/mips/kernel/relocate.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c
> > index 3d80a51..709cfa0 100644
> > --- a/arch/mips/kernel/relocate.c
> > +++ b/arch/mips/kernel/relocate.c
> > @@ -95,7 +95,7 @@ static int __init apply_r_mips_26_rel(u32 *loc_orig, u32 *loc_new, long offset)
> >   
> >   	/* Original target address */
> >   	target_addr <<= 2;
> > -	target_addr += (unsigned long)loc_orig & ~0x03ffffff;
> > +	target_addr += (unsigned long)loc_orig & ~0x0fffffff;
> how about using
>
> 	target_addr += (unsigned long)log_orig & 0xf0000000;
>
> which makes it IMHO even clearer what this does ?
That sounds good. I'll send v2 later.

Thanks,
Jinyang.

> Thomas.