Re: [PATCH v2 27/37] arm64: mte: Switch GCR_EL1 in kernel entry and exit

[Catalin Marinas]

On Thu, Sep 17, 2020 at 05:52:21PM +0100, Catalin Marinas wrote:
> On Tue, Sep 15, 2020 at 11:16:09PM +0200, Andrey Konovalov wrote:
> > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> > index ff34461524d4..79a6848840bd 100644
> > --- a/arch/arm64/kernel/entry.S
> > +++ b/arch/arm64/kernel/entry.S
> > @@ -175,6 +175,28 @@ alternative_else_nop_endif
> >  #endif
> >  	.endm
> >  
> > +	.macro mte_restore_gcr, el, tsk, tmp, tmp2
> > +#ifdef CONFIG_ARM64_MTE
> > +alternative_if_not ARM64_MTE
> > +	b	1f
> > +alternative_else_nop_endif
> > +	.if	\el == 0
> > +	ldr	\tmp, [\tsk, #THREAD_GCR_EL1_USER]
> > +	.else
> > +	ldr_l	\tmp, gcr_kernel_excl
> > +	.endif
> > +	/*
> > +	 * Calculate and set the exclude mask preserving
> > +	 * the RRND (bit[16]) setting.
> > +	 */
> > +	mrs_s	\tmp2, SYS_GCR_EL1
> > +	bfi	\tmp2, \tmp, #0, #16
> > +	msr_s	SYS_GCR_EL1, \tmp2
> > +	isb
> > +1:
> > +#endif
> > +	.endm
> > +
> >  	.macro	kernel_entry, el, regsize = 64
> >  	.if	\regsize == 32
> >  	mov	w0, w0				// zero upper 32 bits of x0
> > @@ -214,6 +236,8 @@ alternative_else_nop_endif
> >  
> >  	ptrauth_keys_install_kernel tsk, x20, x22, x23
> >  
> > +	mte_restore_gcr 1, tsk, x22, x23
> > +
> >  	scs_load tsk, x20
> >  	.else
> >  	add	x21, sp, #S_FRAME_SIZE
> > @@ -332,6 +356,8 @@ alternative_else_nop_endif
> >  	/* No kernel C function calls after this as user keys are set. */
> >  	ptrauth_keys_install_user tsk, x0, x1, x2
> >  
> > +	mte_restore_gcr 0, tsk, x0, x1
> 
> Some nitpicks on these macros to match the ptrauth_keys_* above. Define
> separate mte_set_{user,kernel}_gcr macros with a common mte_set_gcr that
> is used by both.

One more thing - the new mte_set_kernel_gcr should probably skip the
GCR_EL1 update if KASAN_HW_TAGS is disabled.

-- 
Catalin