Re: [PATCH v6 4/4] sparc64: Add support for ADI (Application Data Integrity)

[Anthony Yznaga]

> On Feb 28, 2017, at 10:35 AM, Khalid Aziz <khalid.aziz@xxxxxxxxxx> wrote:
> 
> diff --git a/arch/sparc/kernel/etrap_64.S b/arch/sparc/kernel/etrap_64.S
> index 1276ca2..7be33bf 100644
> --- a/arch/sparc/kernel/etrap_64.S
> +++ b/arch/sparc/kernel/etrap_64.S
> @@ -132,7 +132,33 @@ etrap_save:	save	%g2, -STACK_BIAS, %sp
> 		stx	%g6, [%sp + PTREGS_OFF + PT_V9_G6]
> 		stx	%g7, [%sp + PTREGS_OFF + PT_V9_G7]
> 		or	%l7, %l0, %l7
> -		sethi	%hi(TSTATE_TSO | TSTATE_PEF), %l0
> +661:		sethi	%hi(TSTATE_TSO | TSTATE_PEF), %l0
> +		/*
> +		 * If userspace is using ADI, it could potentially pass
> +		 * a pointer with version tag embedded in it. To maintain
> +		 * the ADI security, we must enable PSTATE.mcde. Userspace
> +		 * would have already set TTE.mcd in an earlier call to
> +		 * kernel and set the version tag for the address being
> +		 * dereferenced. Setting PSTATE.mcde would ensure any
> +		 * access to userspace data through a system call honors
> +		 * ADI and does not allow a rogue app to bypass ADI by
> +		 * using system calls. Setting PSTATE.mcde only affects
> +		 * accesses to virtual addresses that have TTE.mcd set.
> +		 * Set PMCDPER to ensure any exceptions caused by ADI
> +		 * version tag mismatch are exposed before system call
> +		 * returns to userspace. Setting PMCDPER affects only
> +		 * writes to virtual addresses that have TTE.mcd set and
> +		 * have a version tag set as well.
> +		 */
> +		.section .sun_m7_1insn_patch, "ax"
> +		.word	661b
> +		sethi	%hi(TSTATE_TSO | TSTATE_PEF | TSTATE_MCDE), %l0
> +		.previous
> +661:		nop
> +		.section .sun_m7_1insn_patch, "ax"
> +		.word	661b
> +		.word 0xaf902001	/* wrpr %g0, 1, %pmcdper */

Since PMCDPER is never cleared, setting it here is quickly going to set it on all CPUs and then become an expensive "nop" that burns ~50 cycles each time through etrap.  Consider setting it at boot time and when a CPU is DR'd into the system.

Anthony