Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linu…

…x/kernel/git/tip/tip

Pull x86 pti fixes from Thomas Gleixner:
 "A set of updates for the x86/pti related code:

   - Preserve r8-r11 in int $0x80. r8-r11 need to be preserved, but the
     int$80 entry code removed that quite some time ago. Make it correct
     again.

   - A set of fixes for the Global Bit work which went into 4.17 and
     caused a bunch of interesting regressions:

      - Triggering a BUG in the page attribute code due to a missing
        check for early boot stage

      - Warnings in the page attribute code about holes in the kernel
        text mapping which are caused by the freeing of the init code.
        Handle such holes gracefully.

      - Reduce the amount of kernel memory which is set global to the
        actual text and do not incidentally overlap with data.

      - Disable the global bit when RANDSTRUCT is enabled as it
        partially defeats the hardening.

      - Make the page protection setup correct for vma->page_prot
        population again. The adjustment of the protections fell through
        the crack during the Global bit rework and triggers warnings on
        machines which do not support certain features, e.g. NX"

* 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/entry/64/compat: Preserve r8-r11 in int $0x80
  x86/pti: Filter at vma->vm_page_prot population
  x86/pti: Disallow global kernel text with RANDSTRUCT
  x86/pti: Reduce amount of kernel text allowed to be Global
  x86/pti: Fix boot warning from Global-bit setting
  x86/pti: Fix boot problems from Global-bit setting

arch/x86/Kconfig

@@ -52,6 +52,7 @@ config X86
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_FAST_MULTIPLIER
+	select ARCH_HAS_FILTER_PGPROT
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_KCOV			if X86_64
@@ -273,6 +274,9 @@ config ARCH_HAS_CPU_RELAX
 config ARCH_HAS_CACHE_LINE_SIZE
 	def_bool y
 
+config ARCH_HAS_FILTER_PGPROT
+	def_bool y
+
 config HAVE_SETUP_PER_CPU_AREA
 	def_bool y
 

arch/x86/entry/entry_64_compat.S

@@ -84,13 +84,13 @@ ENTRY(entry_SYSENTER_compat)
 	pushq	%rdx			/* pt_regs->dx */
 	pushq	%rcx			/* pt_regs->cx */
 	pushq	$-ENOSYS		/* pt_regs->ax */
-	pushq   $0			/* pt_regs->r8  = 0 */
+	pushq   %r8			/* pt_regs->r8 */
 	xorl	%r8d, %r8d		/* nospec   r8 */
-	pushq   $0			/* pt_regs->r9  = 0 */
+	pushq   %r9			/* pt_regs->r9 */
 	xorl	%r9d, %r9d		/* nospec   r9 */
-	pushq   $0			/* pt_regs->r10 = 0 */
+	pushq   %r10			/* pt_regs->r10 */
 	xorl	%r10d, %r10d		/* nospec   r10 */
-	pushq   $0			/* pt_regs->r11 = 0 */
+	pushq   %r11			/* pt_regs->r11 */
 	xorl	%r11d, %r11d		/* nospec   r11 */
 	pushq   %rbx                    /* pt_regs->rbx */
 	xorl	%ebx, %ebx		/* nospec   rbx */

arch/x86/include/asm/pgtable.h

@@ -601,6 +601,11 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 
 #define canon_pgprot(p) __pgprot(massage_pgprot(p))
 
+static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
+{
+	return canon_pgprot(prot);
+}
+
 static inline int is_new_memtype_allowed(u64 paddr, unsigned long size,
 					 enum page_cache_mode pcm,
 					 enum page_cache_mode new_pcm)

arch/x86/mm/pageattr.c

@@ -93,6 +93,18 @@ void arch_report_meminfo(struct seq_file *m)
 static inline void split_page_count(int level) { }
 #endif
 
+static inline int
+within(unsigned long addr, unsigned long start, unsigned long end)
+{
+	return addr >= start && addr < end;
+}
+
+static inline int
+within_inclusive(unsigned long addr, unsigned long start, unsigned long end)
+{
+	return addr >= start && addr <= end;
+}
+
 #ifdef CONFIG_X86_64
 
 static inline unsigned long highmap_start_pfn(void)
@@ -106,20 +118,25 @@ static inline unsigned long highmap_end_pfn(void)
 	return __pa_symbol(roundup(_brk_end, PMD_SIZE) - 1) >> PAGE_SHIFT;
 }
 
-#endif
-
-static inline int
-within(unsigned long addr, unsigned long start, unsigned long end)
+static bool __cpa_pfn_in_highmap(unsigned long pfn)
 {
-	return addr >= start && addr < end;
+	/*
+	 * Kernel text has an alias mapping at a high address, known
+	 * here as "highmap".
+	 */
+	return within_inclusive(pfn, highmap_start_pfn(), highmap_end_pfn());
 }
 
-static inline int
-within_inclusive(unsigned long addr, unsigned long start, unsigned long end)
+#else
+
+static bool __cpa_pfn_in_highmap(unsigned long pfn)
 {
-	return addr >= start && addr <= end;
+	/* There is no highmap on 32-bit */
+	return false;
 }
 
+#endif
+
 /*
  * Flushing functions
  */
@@ -172,7 +189,7 @@ static void __cpa_flush_all(void *arg)
 
 static void cpa_flush_all(unsigned long cache)
 {
-	BUG_ON(irqs_disabled());
+	BUG_ON(irqs_disabled() && !early_boot_irqs_disabled);
 
 	on_each_cpu(__cpa_flush_all, (void *) cache, 1);
 }
@@ -236,7 +253,7 @@ static void cpa_flush_array(unsigned long *start, int numpages, int cache,
 	unsigned long do_wbinvd = cache && numpages >= 1024; /* 4M threshold */
 #endif
 
-	BUG_ON(irqs_disabled());
+	BUG_ON(irqs_disabled() && !early_boot_irqs_disabled);
 
 	on_each_cpu(__cpa_flush_all, (void *) do_wbinvd, 1);
 
@@ -1183,6 +1200,10 @@ static int __cpa_process_fault(struct cpa_data *cpa, unsigned long vaddr,
 		cpa->numpages = 1;
 		cpa->pfn = __pa(vaddr) >> PAGE_SHIFT;
 		return 0;
+
+	} else if (__cpa_pfn_in_highmap(cpa->pfn)) {
+		/* Faults in the highmap are OK, so do not warn: */
+		return -EFAULT;
 	} else {
 		WARN(1, KERN_WARNING "CPA: called for zero pte. "
 			"vaddr = %lx cpa->vaddr = %lx\n", vaddr,
@@ -1335,8 +1356,7 @@ static int cpa_process_alias(struct cpa_data *cpa)
 	 * to touch the high mapped kernel as well:
 	 */
 	if (!within(vaddr, (unsigned long)_text, _brk_end) &&
-	    within_inclusive(cpa->pfn, highmap_start_pfn(),
-			     highmap_end_pfn())) {
+	    __cpa_pfn_in_highmap(cpa->pfn)) {
 		unsigned long temp_cpa_vaddr = (cpa->pfn << PAGE_SHIFT) +
 					       __START_KERNEL_map - phys_base;
 		alias_cpa = *cpa;

arch/x86/mm/pti.c

@@ -421,6 +421,16 @@ static inline bool pti_kernel_image_global_ok(void)
 	if (boot_cpu_has(X86_FEATURE_K8))
 		return false;
 
+	/*
+	 * RANDSTRUCT derives its hardening benefits from the
+	 * attacker's lack of knowledge about the layout of kernel
+	 * data structures.  Keep the kernel image non-global in
+	 * cases where RANDSTRUCT is in use to help keep the layout a
+	 * secret.
+	 */
+	if (IS_ENABLED(CONFIG_GCC_PLUGIN_RANDSTRUCT))
+		return false;
+
 	return true;
 }
 
@@ -430,12 +440,24 @@ static inline bool pti_kernel_image_global_ok(void)
  */
 void pti_clone_kernel_text(void)
 {
+	/*
+	 * rodata is part of the kernel image and is normally
+	 * readable on the filesystem or on the web.  But, do not
+	 * clone the areas past rodata, they might contain secrets.
+	 */
 	unsigned long start = PFN_ALIGN(_text);
-	unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE);
+	unsigned long end = (unsigned long)__end_rodata_hpage_align;
 
 	if (!pti_kernel_image_global_ok())
 		return;
 
+	pr_debug("mapping partial kernel image into user address space\n");
+
+	/*
+	 * Note that this will undo _some_ of the work that
+	 * pti_set_kernel_image_nonglobal() did to clear the
+	 * global bit.
+	 */
 	pti_clone_pmds(start, end, _PAGE_RW);
 }
 
@@ -458,8 +480,6 @@ void pti_set_kernel_image_nonglobal(void)
 	if (pti_kernel_image_global_ok())
 		return;
 
-	pr_debug("set kernel image non-global\n");
-
 	set_memory_nonglobal(start, (end - start) >> PAGE_SHIFT);
 }
 

mm/mmap.c

@@ -100,11 +100,20 @@ pgprot_t protection_map[16] __ro_after_init = {
 	__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
 };
 
+#ifndef CONFIG_ARCH_HAS_FILTER_PGPROT
+static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
+{
+	return prot;
+}
+#endif
+
 pgprot_t vm_get_page_prot(unsigned long vm_flags)
 {
-	return __pgprot(pgprot_val(protection_map[vm_flags &
+	pgprot_t ret = __pgprot(pgprot_val(protection_map[vm_flags &
 				(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
 			pgprot_val(arch_vm_get_page_prot(vm_flags)));
+
+	return arch_filter_pgprot(ret);
 }
 EXPORT_SYMBOL(vm_get_page_prot);
 

tools/testing/selftests/x86/test_syscall_vdso.c

@@ -100,12 +100,19 @@ asm (
 	"	shl	$32, %r8\n"
 	"	orq	$0x7f7f7f7f, %r8\n"
 	"	movq	%r8, %r9\n"
-	"	movq	%r8, %r10\n"
-	"	movq	%r8, %r11\n"
-	"	movq	%r8, %r12\n"
-	"	movq	%r8, %r13\n"
-	"	movq	%r8, %r14\n"
-	"	movq	%r8, %r15\n"
+	"	incq	%r9\n"
+	"	movq	%r9, %r10\n"
+	"	incq	%r10\n"
+	"	movq	%r10, %r11\n"
+	"	incq	%r11\n"
+	"	movq	%r11, %r12\n"
+	"	incq	%r12\n"
+	"	movq	%r12, %r13\n"
+	"	incq	%r13\n"
+	"	movq	%r13, %r14\n"
+	"	incq	%r14\n"
+	"	movq	%r14, %r15\n"
+	"	incq	%r15\n"
 	"	ret\n"
 	"	.code32\n"
 	"	.popsection\n"
@@ -128,12 +135,13 @@ int check_regs64(void)
 	int err = 0;
 	int num = 8;
 	uint64_t *r64 = &regs64.r8;
+	uint64_t expected = 0x7f7f7f7f7f7f7f7fULL;
 
 	if (!kernel_is_64bit)
 		return 0;
 
 	do {
-		if (*r64 == 0x7f7f7f7f7f7f7f7fULL)
+		if (*r64 == expected++)
 			continue; /* register did not change */
 		if (syscall_addr != (long)&int80) {
 			/*
@@ -147,18 +155,17 @@ int check_regs64(void)
 				continue;
 			}
 		} else {
-			/* INT80 syscall entrypoint can be used by
+			/*
+			 * INT80 syscall entrypoint can be used by
 			 * 64-bit programs too, unlike SYSCALL/SYSENTER.
 			 * Therefore it must preserve R12+
 			 * (they are callee-saved registers in 64-bit C ABI).
 			 *
-			 * This was probably historically not intended,
-			 * but R8..11 are clobbered (cleared to 0).
-			 * IOW: they are the only registers which aren't
-			 * preserved across INT80 syscall.
+			 * Starting in Linux 4.17 (and any kernel that
+			 * backports the change), R8..11 are preserved.
+			 * Historically (and probably unintentionally), they
+			 * were clobbered or zeroed.
 			 */
-			if (*r64 == 0 && num <= 11)
-				continue;
 		}
 		printf("[FAIL]\tR%d has changed:%016llx\n", num, *r64);
 		err++;