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pc64: implement NX bit discovery, map kernel mappings no-execute

--- a/sys/src/9/pc/dat.h

+++ b/sys/src/9/pc/dat.h

@@ -244,6 +244,7 @@

 	int	havetsc;

 	int	havepge;

 	int	havewatchpt8;

+	int	havenx;

 	uvlong	tscticks;

 	int	pdballoc;

 	int	pdbfree;

--- a/sys/src/9/pc/devarch.c

+++ b/sys/src/9/pc/devarch.c

@@ -899,10 +899,26 @@

 	else

 		hwrandbuf = nil;

-	/* 8-byte watchpoints are supported in Long Mode */

-	if(sizeof(uintptr) == 8)

+	if(sizeof(uintptr) == 8) {

+		/* 8-byte watchpoints are supported in Long Mode */

 		m->havewatchpt8 = 1;

-	else if(strcmp(m->cpuidid, "GenuineIntel") == 0){

+

+		/* check and enable NX bit */

+		cpuid(Highextfunc, regs);

+		if(regs[0] >= Procextfeat){

+			cpuid(Procextfeat, regs);

+			if((regs[3] & (1<<20)) != 0){

+				vlong efer;

+

+				/* enable no-execute feature */

+				if(rdmsr(Efer, &efer) != -1){

+					efer |= 1ull<<11;

+					if(wrmsr(Efer, efer) != -1)

+						m->havenx = 1;

+				}

+			}

+		}

+	} else if(strcmp(m->cpuidid, "GenuineIntel") == 0){

 		/* some random CPUs that support 8-byte watchpoints */

 		if(family == 15 && (model == 3 || model == 4 || model == 6)

 		|| family == 6 && (model == 15 || model == 23 || model == 28))

--- a/sys/src/9/pc64/dat.h

+++ b/sys/src/9/pc64/dat.h

@@ -222,6 +222,7 @@

 	int	havetsc;

 	int	havepge;

 	int	havewatchpt8;

+	int	havenx;

 	uvlong	tscticks;

 	u64int	dr7;			/* shadow copy of dr7 */

--- a/sys/src/9/pc64/mem.h

+++ b/sys/src/9/pc64/mem.h

@@ -143,7 +143,7 @@

 #define	PTEPERTAB	(PTEMAPMEM/BY2PG)

 #define	SEGMAPSIZE	65536

 #define	SSEGMAPSIZE	16

-#define	PPN(x)		((x)&~(BY2PG-1))

+#define	PPN(x)		((x)&~(1ull<<63 | BY2PG-1))

 /*

  *  physical MMU

@@ -158,6 +158,7 @@

 #define	PTEUSER		(1ull<<2)

 #define	PTESIZE		(1ull<<7)

 #define	PTEGLOBAL	(1ull<<8)

+#define	PTENOEXEC	((uvlong)m->havenx<<63)

 /*

  * Hierarchical Page Tables.

--- a/sys/src/9/pc64/mmu.c

+++ b/sys/src/9/pc64/mmu.c

@@ -116,24 +116,19 @@

 	taskswitch((uintptr)m + MACHSIZE);

 	ltr(TSSSEL);

-	wrmsr(0xc0000100, 0ull);	/* 64 bit fsbase */

-	wrmsr(0xc0000101, (uvlong)&machp[m->machno]);	/* 64 bit gsbase */

-	wrmsr(0xc0000102, 0ull);	/* kernel gs base */

+	wrmsr(FSbase, 0ull);

+	wrmsr(GSbase, (uvlong)&machp[m->machno]);

+	wrmsr(KernelGSbase, 0ull);

 	/* enable syscall extension */

-	rdmsr(0xc0000080, &v);

+	rdmsr(Efer, &v);

 	v |= 1ull;

-	wrmsr(0xc0000080, v);

+	wrmsr(Efer, v);

-	/* IA32_STAR */

-	wrmsr(0xc0000081, ((uvlong)UE32SEL << 48) | ((uvlong)KESEL << 32));

+	wrmsr(Star, ((uvlong)UE32SEL << 48) | ((uvlong)KESEL << 32));

+	wrmsr(Lstar, (uvlong)syscallentry);

+	wrmsr(Sfmask, 0x200);

-	/* IA32_LSTAR */

-	wrmsr(0xc0000082, (uvlong)syscallentry);

-

-	/* SYSCALL flags mask */

-	wrmsr(0xc0000084, 0x200);

-

 	/* IA32_PAT write combining */

 	if((MACHP(0)->cpuiddx & Pat) != 0

 	&& rdmsr(0x277, &v) != -1){

@@ -443,7 +438,7 @@

 	if(pte == 0)

 		panic("putmmu: bug: va=%#p pa=%#p", va, pa);

 	old = *pte;

-	*pte = pa | PTEVALID|PTEUSER;

+	*pte = pa | PTEUSER;

 	splx(x);

 	if(old & PTEVALID)

 		invlpg(va);

@@ -487,7 +482,7 @@

 	pte = mmuwalk(m->pml4, va, 0, 1);

 	if(pte == 0 || (*pte & PTEVALID) != 0)

 		panic("kmap: pa=%#p va=%#p", pa, va);

-	*pte = pa | PTEWRITE|PTEVALID;

+	*pte = pa | PTEWRITE|PTENOEXEC|PTEVALID;

 	splx(x);

 	invlpg(va);

 	return (KMap*)va;

@@ -533,7 +528,7 @@

 	pa -= o;

 	va -= o;

 	size += o;

-	pmap(m->pml4, pa | PTEUNCACHED|PTEWRITE|PTEVALID, va, size);

+	pmap(m->pml4, pa | PTEUNCACHED|PTEWRITE|PTENOEXEC|PTEVALID, va, size);

 	return (void*)(va+o);

 }

@@ -616,7 +611,7 @@

 			pm->npage = (top - pm->base)/BY2PG;

 			va = base + VMAP;

-			pmap(m->pml4, base | PTEGLOBAL|PTEWRITE|PTEVALID, va, psize);

+			pmap(m->pml4, base | PTEGLOBAL|PTEWRITE|PTENOEXEC|PTEVALID, va, psize);

 			palloc.pages = (void*)(va + tsize);