Re: [PATCH v2] x86/mm: Refuse W^X violations

[Dave Hansen]

On 9/22/22 00:46, Peter Zijlstra wrote:
> On Wed, Sep 21, 2022 at 08:09:13PM -0700, Guenter Roeck wrote:
> 
>> Oh well, that "helped" to hide one of the crashes. Here is another one.
>> This is with PAE enabled and booting through efi32.
> 
>> [    1.086592]  efi_runtime_update_mappings+0x36/0x42
>> [    1.086717]  efi_enter_virtual_mode+0x351/0x36e
>> [    1.086860]  start_kernel+0x57d/0x60f
>> [    1.086956]  ? set_intr_gate+0x42/0x55
>> [    1.087079]  i386_start_kernel+0x43/0x45
>> [    1.087272]  startup_32_smp+0x161/0x164
> 
> Does this help? Dave; perhaps we should just let i386 be i386 and let it
> bitrot :/

How about we just turn off enforcement for now so that the poor i386
folks can at least boot?  I have the feeling we're going to get bored
with even the warnings if they persist for too long, though.

Untested patch to make i386 violations harmless is attached.diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 20b1e24baa85..c899c55d8304 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -585,6 +585,8 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long start,
 static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long start,
 				  unsigned long pfn, unsigned long npg)
 {
+	/* Just warn on i386, there are still too many issues there: */
+	bool refuse = IS_ENABLED(CONFIG_X86_64);
 	unsigned long end;
 
 	/* Only enforce when NX is supported: */
@@ -598,13 +600,17 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star
 		return new;
 
 	end = start + npg * PAGE_SIZE - 1;
-	WARN_ONCE(1, "CPA refuse W^X violation: %016llx -> %016llx range: 0x%016lx - 0x%016lx PFN %lx\n",
+	WARN_ONCE(1, "CPA %sW^X violation: %016llx -> %016llx range: 0x%016lx - 0x%016lx PFN %lx\n",
+		  refuse ? "refuse " : "",
 		  (unsigned long long)pgprot_val(old),
 		  (unsigned long long)pgprot_val(new),
 		  start, end, pfn);
 
 	/* refuse the transition into WX */
-	return old;
+	if (refuse)
+		return old;
+
+	return new;
 }
 
 /*