Re: [PATCH 5/9] x86/mm/pat: don't warn about W^X violations before mark_rodata_ro()

[Mike Rapoport <rppt@kernel.org>]

Hi Salvatore,

On Thu, Nov 12, 2026 at 10:46:03PM +0100, Salvatore Bonaccorso wrote:
> Hi Mike,
> 
> On Thu, Nov 12, 2026 at 06:31:10PM +0200, Mike Rapoport (Microsoft) wrote:
> > The kernel text is mapped RWX until mark_rodata_ro(), so W^X violations
> > that verify_rwx() detects before that can be false positives.
> > 
> > CHECK_WX is enabled by default with STRICT_KERNEL_RWX and it reports
> > mappings that remain W+X after mark_rodata_ro().
> > 
> > Drop the warning about W^X violations before mark_rodata_ro().
> > 
> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> > ---
> >  arch/x86/mm/pat/set_memory.c | 18 ++++++------------
> >  1 file changed, 6 insertions(+), 12 deletions(-)
> > 
> > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> > index a1bea16a3c3bb..a674433850dc9 100644
> > --- a/arch/x86/mm/pat/set_memory.c
> > +++ b/arch/x86/mm/pat/set_memory.c
> > @@ -718,21 +718,15 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star
> >  	if (!rw || nx)
> >  		return new;
> >  
> > -	end = start + npg * PAGE_SIZE - 1;
> > -
> >  	/*
> > -	 * If the kernel text is still RWX, gently complain, this could be a
> > -	 * false positive.
> > -	 * Once debug_checkwx() becomes mandatory for CONFIG_STRICT_KERNEL_RWX,
> > -	 * the warning can be removed completely.
> > +	 * The kernel text is RWX until mark_rodata_ro() and the entire kernel
> > +	 * page table is verified after the text is protected, so there is no
> > +	 * need to warn.
> >  	 */
> > -	if (!kernel_set_to_readonly) {
> > -		pr_warn_once("CPA detected W^X violation: %016llx -> %016llx range: 0x%016lx - 0x%016lx PFN %lx\n",
> > -		  (unsigned long long)pgprot_val(old),
> > -		  (unsigned long long)pgprot_val(new),
> > -		  start, end, pfn);
> > +	if (!kernel_set_to_readonly)
> >  		return new;
> > -	}
> > +
> > +	end = start + npg * PAGE_SIZE - 1;
> >  
> >  	WARN_ONCE(1, "CPA detected W^X violation: %016llx -> %016llx range: 0x%016lx - 0x%016lx PFN %lx\n",
> >  		  (unsigned long long)pgprot_val(old),
> > 
> > -- 
> > 2.53.0
> 
> Does this need to carry a 
> 
> Fixes: ea6fd393cb9e ("x86/mm/pat: Use pr_warn() for early W^X warnings")

No, that commit actually relaxes how W^X violations are reported during
early boot.

And this patch removes the warning only because there is an earlier commit
that forces the check of W^X consistency that was optional previously.
 
> ? 
> 
> On a system booted into 6.12.117 (from 6.12.116) I see:
> 
> [    1.091378] ------------[ cut here ]------------
> [    1.092538] CPA detected W^X violation: 0000000000000121 -> 0000000000000123 range: 0xffffffffc0477000 - 0xffffffffc0477fff PFN 109c1f
> [    1.093994] WARNING: CPU: 5 PID: 222 at arch/x86/mm/pat/set_memory.c:665 __change_page_attr_set_clr+0xf62/0xfb0

Please see my reply to your regression report.

> Regards,
> Salvatore

-- 
Sincerely yours,
Mike.