On Thu, Nov 30, 2017 at 04:39:34PM +0000, Will Deacon wrote:
> With the ASID now installed in TTBR1, we can re-enable ARM64_SW_TTBR0_PAN
> by ensuring that we switch to a reserved ASID of zero when disabling
> user access and restore the active user ASID on the uaccess enable path.
>
> Signed-off-by: Will Deacon <[email protected]>
[...]
> diff --git a/arch/arm64/include/asm/asm-uaccess.h
> b/arch/arm64/include/asm/asm-uaccess.h
> index b3da6c886835..21b8cf304028 100644
> --- a/arch/arm64/include/asm/asm-uaccess.h
> +++ b/arch/arm64/include/asm/asm-uaccess.h
> @@ -16,11 +16,20 @@
> add \tmp1, \tmp1, #SWAPPER_DIR_SIZE // reserved_ttbr0 at the end of
> swapper_pg_dir
> msr ttbr0_el1, \tmp1 // set reserved TTBR0_EL1
> isb
> + sub \tmp1, \tmp1, #SWAPPER_DIR_SIZE
> + bic \tmp1, \tmp1, #(0xffff << 48)
> + msr ttbr1_el1, \tmp1 // set reserved ASID
> + isb
> .endm
>
> - .macro __uaccess_ttbr0_enable, tmp1
> + .macro __uaccess_ttbr0_enable, tmp1, tmp2
> get_thread_info \tmp1
> ldr \tmp1, [\tmp1, #TSK_TI_TTBR0] // load saved TTBR0_EL1
> + mrs \tmp2, ttbr1_el1
> + extr \tmp2, \tmp2, \tmp1, #48
> + ror \tmp2, \tmp2, #16
It took me a while to figure out what was going on here, as I confused
EXTR with BFX.
I also didn't realise that thread_info::ttbr0 still had the ASID
orred-in. I guess it doesn't matter if we write that into TTBR0_EL1, as
it should be ignored by HW.
> diff --git a/arch/arm64/include/asm/uaccess.h
> b/arch/arm64/include/asm/uaccess.h
> index fc0f9eb66039..750a3b76a01c 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -107,15 +107,19 @@ static inline void __uaccess_ttbr0_disable(void)
> {
> unsigned long ttbr;
>
> + ttbr = read_sysreg(ttbr1_el1);
> /* reserved_ttbr0 placed at the end of swapper_pg_dir */
> - ttbr = read_sysreg(ttbr1_el1) + SWAPPER_DIR_SIZE;
> - write_sysreg(ttbr, ttbr0_el1);
> + write_sysreg(ttbr + SWAPPER_DIR_SIZE, ttbr0_el1);
> + isb();
> + /* Set reserved ASID */
> + ttbr &= ~(0xffffUL << 48);
Given we have this constant open-coded in a few places, maybe we should
have something like:
#define TTBR_ASID_MASK (UL(0xffff) << 48)
... in a header somewhere.
Otherwise, looks good to me.
Thanks,
Mark.
