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SubjectRe: [PATCH 1/3] MIPS: KASLR: Correcte valid bits in apply_r_mips_26_rel
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@loongson.cn>
> ---
> 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 ?

Thomas.

--
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea. [ RFC1925, 2.3 ]

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