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SubjectRe: [RFC v6 27/62] powerpc: helper to validate key-access permissions of a pte
Date

Ram Pai <linuxram@us.ibm.com> writes:
> --- a/arch/powerpc/mm/pkeys.c
> +++ b/arch/powerpc/mm/pkeys.c
> @@ -201,3 +201,36 @@ int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
> */
> return vma_pkey(vma);
> }
> +
> +static bool pkey_access_permitted(int pkey, bool write, bool execute)
> +{
> + int pkey_shift;
> + u64 amr;
> +
> + if (!pkey)
> + return true;
> +
> + pkey_shift = pkeyshift(pkey);
> + if (!(read_uamor() & (0x3UL << pkey_shift)))
> + return true;
> +
> + if (execute && !(read_iamr() & (IAMR_EX_BIT << pkey_shift)))
> + return true;
> +
> + if (!write) {
> + amr = read_amr();
> + if (!(amr & (AMR_RD_BIT << pkey_shift)))
> + return true;
> + }
> +
> + amr = read_amr(); /* delay reading amr uptil absolutely needed */

Actually, this is causing amr to be read twice in case control enters
the "if (!write)" block above but doesn't enter the other if block nested
in it.

read_amr should be called only once, right before "if (!write)".

--
Thiago Jung Bauermann
IBM Linux Technology Center

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