1 files changed, 212 insertions, 0 deletions
diff --git a/common/recipes-kernel/linux/linux-yocto-4.9.21/0006-kaiser-do-not-set-_PAGE_NX-on-pgd_none.patch b/common/recipes-kernel/linux/linux-yocto-4.9.21/0006-kaiser-do-not-set-_PAGE_NX-on-pgd_none.patch
new file mode 100644
index 00000000..01f7310c
--- /dev/null
+++ b/common/recipes-kernel/linux/linux-yocto-4.9.21/0006-kaiser-do-not-set-_PAGE_NX-on-pgd_none.patch
@@ -0,0 +1,212 @@
+From 4e010256639fdd9c87743dc7c7ad6a53bc96c1af Mon Sep 17 00:00:00 2001
+From: Hugh Dickins <hughd@google.com>
+Date: Tue, 5 Sep 2017 12:05:01 -0700
+Subject: [PATCH 006/102] kaiser: do not set _PAGE_NX on pgd_none
+
+native_pgd_clear() uses native_set_pgd(), so native_set_pgd() must
+avoid setting the _PAGE_NX bit on an otherwise pgd_none() entry:
+usually that just generated a warning on exit, but sometimes
+more mysterious and damaging failures (our production machines
+could not complete booting).
+
+The original fix to this just avoided adding _PAGE_NX to
+an empty entry; but eventually more problems surfaced with kexec,
+and EFI mapping expected to be a problem too.  So now instead
+change native_set_pgd() to update shadow only if _PAGE_USER:
+
+A few places (kernel/machine_kexec_64.c, platform/efi/efi_64.c for sure)
+use set_pgd() to set up a temporary internal virtual address space, with
+physical pages remapped at what Kaiser regards as userspace addresses:
+Kaiser then assumes a shadow pgd follows, which it will try to corrupt.
+
+This appears to be responsible for the recent kexec and kdump failures;
+though it's unclear how those did not manifest as a problem before.
+Ah, the shadow pgd will only be assumed to "follow" if the requested
+pgd is on an even-numbered page: so I suppose it was going wrong 50%
+of the time all along.
+
+What we need is a flag to set_pgd(), to tell it we're dealing with
+userspace.  Er, isn't that what the pgd's _PAGE_USER bit is saying?
+Add a test for that.  But we cannot do the same for pgd_clear()
+(which may be called to clear corrupted entries - set aside the
+question of "corrupt in which pgd?" until later), so there just
+rely on pgd_clear() not being called in the problematic cases -
+with a WARN_ON_ONCE() which should fire half the time if it is.
+
+But this is getting too big for an inline function: move it into
+arch/x86/mm/kaiser.c (which then demands a boot/compressed mod);
+and de-void and de-space native_get_shadow/normal_pgd() while here.
+
+Also make an unnecessary change to KASLR's init_trampoline(): it was
+using set_pgd() to assign a pgd-value to a global variable (not in a
+pg directory page), which was rather scary given Kaiser's previous
+set_pgd() implementation: not a problem now, but too scary to leave
+as was, it could easily blow up if we have to change set_pgd() again.
+
+Signed-off-by: Hugh Dickins <hughd@google.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/boot/compressed/misc.h   |  1 +
+ arch/x86/include/asm/pgtable_64.h | 51 ++++++++++-----------------------------
+ arch/x86/mm/kaiser.c              | 42 ++++++++++++++++++++++++++++++++
+ arch/x86/mm/kaslr.c               |  4 +--
+ 4 files changed, 58 insertions(+), 40 deletions(-)
+
+diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
+index 1c8355e..cd80024 100644
+--- a/arch/x86/boot/compressed/misc.h
++++ b/arch/x86/boot/compressed/misc.h
+@@ -9,6 +9,7 @@
+  */
+ #undef CONFIG_PARAVIRT
+ #undef CONFIG_PARAVIRT_SPINLOCKS
++#undef CONFIG_KAISER
+ #undef CONFIG_KASAN
+ 
+ #include <linux/linkage.h>
+diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
+index 000265c..177caf3 100644
+--- a/arch/x86/include/asm/pgtable_64.h
++++ b/arch/x86/include/asm/pgtable_64.h
+@@ -107,61 +107,36 @@ static inline void native_pud_clear(pud_t *pud)
+ }
+ 
+ #ifdef CONFIG_KAISER
+-static inline pgd_t * native_get_shadow_pgd(pgd_t *pgdp)
++extern pgd_t kaiser_set_shadow_pgd(pgd_t *pgdp, pgd_t pgd);
++
++static inline pgd_t *native_get_shadow_pgd(pgd_t *pgdp)
+ {
+-	return (pgd_t *)(void*)((unsigned long)(void*)pgdp | (unsigned long)PAGE_SIZE);
++	return (pgd_t *)((unsigned long)pgdp | (unsigned long)PAGE_SIZE);
+ }
+ 
+-static inline pgd_t * native_get_normal_pgd(pgd_t *pgdp)
++static inline pgd_t *native_get_normal_pgd(pgd_t *pgdp)
+ {
+-	return (pgd_t *)(void*)((unsigned long)(void*)pgdp &  ~(unsigned long)PAGE_SIZE);
++	return (pgd_t *)((unsigned long)pgdp & ~(unsigned long)PAGE_SIZE);
+ }
+ #else
+-static inline pgd_t * native_get_shadow_pgd(pgd_t *pgdp)
++static inline pgd_t kaiser_set_shadow_pgd(pgd_t *pgdp, pgd_t pgd)
++{
++	return pgd;
++}
++static inline pgd_t *native_get_shadow_pgd(pgd_t *pgdp)
+ {
+ 	BUILD_BUG_ON(1);
+ 	return NULL;
+ }
+-static inline pgd_t * native_get_normal_pgd(pgd_t *pgdp)
++static inline pgd_t *native_get_normal_pgd(pgd_t *pgdp)
+ {
+ 	return pgdp;
+ }
+ #endif /* CONFIG_KAISER */
+ 
+-/*
+- * Page table pages are page-aligned.  The lower half of the top
+- * level is used for userspace and the top half for the kernel.
+- * This returns true for user pages that need to get copied into
+- * both the user and kernel copies of the page tables, and false
+- * for kernel pages that should only be in the kernel copy.
+- */
+-static inline bool is_userspace_pgd(void *__ptr)
+-{
+-	unsigned long ptr = (unsigned long)__ptr;
+-
+-	return ((ptr % PAGE_SIZE) < (PAGE_SIZE / 2));
+-}
+-
+ static inline void native_set_pgd(pgd_t *pgdp, pgd_t pgd)
+ {
+-#ifdef CONFIG_KAISER
+-	pteval_t extra_kern_pgd_flags = 0;
+-	/* Do we need to also populate the shadow pgd? */
+-	if (is_userspace_pgd(pgdp)) {
+-		native_get_shadow_pgd(pgdp)->pgd = pgd.pgd;
+-		/*
+-		 * Even if the entry is *mapping* userspace, ensure
+-		 * that userspace can not use it.  This way, if we
+-		 * get out to userspace running on the kernel CR3,
+-		 * userspace will crash instead of running.
+-		 */
+-		extra_kern_pgd_flags = _PAGE_NX;
+-	}
+-	pgdp->pgd = pgd.pgd;
+-	pgdp->pgd |= extra_kern_pgd_flags;
+-#else /* CONFIG_KAISER */
+-	*pgdp = pgd;
+-#endif
++	*pgdp = kaiser_set_shadow_pgd(pgdp, pgd);
+ }
+ 
+ static inline void native_pgd_clear(pgd_t *pgd)
+diff --git a/arch/x86/mm/kaiser.c b/arch/x86/mm/kaiser.c
+index 7270a29..8d6061c 100644
+--- a/arch/x86/mm/kaiser.c
++++ b/arch/x86/mm/kaiser.c
+@@ -302,4 +302,46 @@ void kaiser_remove_mapping(unsigned long start, unsigned long size)
+ 		unmap_pud_range_nofree(pgd, addr, end);
+ 	}
+ }
++
++/*
++ * Page table pages are page-aligned.  The lower half of the top
++ * level is used for userspace and the top half for the kernel.
++ * This returns true for user pages that need to get copied into
++ * both the user and kernel copies of the page tables, and false
++ * for kernel pages that should only be in the kernel copy.
++ */
++static inline bool is_userspace_pgd(pgd_t *pgdp)
++{
++	return ((unsigned long)pgdp % PAGE_SIZE) < (PAGE_SIZE / 2);
++}
++
++pgd_t kaiser_set_shadow_pgd(pgd_t *pgdp, pgd_t pgd)
++{
++	/*
++	 * Do we need to also populate the shadow pgd?  Check _PAGE_USER to
++	 * skip cases like kexec and EFI which make temporary low mappings.
++	 */
++	if (pgd.pgd & _PAGE_USER) {
++		if (is_userspace_pgd(pgdp)) {
++			native_get_shadow_pgd(pgdp)->pgd = pgd.pgd;
++			/*
++			 * Even if the entry is *mapping* userspace, ensure
++			 * that userspace can not use it.  This way, if we
++			 * get out to userspace running on the kernel CR3,
++			 * userspace will crash instead of running.
++			 */
++			pgd.pgd |= _PAGE_NX;
++		}
++	} else if (!pgd.pgd) {
++		/*
++		 * pgd_clear() cannot check _PAGE_USER, and is even used to
++		 * clear corrupted pgd entries: so just rely on cases like
++		 * kexec and EFI never to be using pgd_clear().
++		 */
++		if (!WARN_ON_ONCE((unsigned long)pgdp & PAGE_SIZE) &&
++		    is_userspace_pgd(pgdp))
++			native_get_shadow_pgd(pgdp)->pgd = pgd.pgd;
++	}
++	return pgd;
++}
+ #endif /* CONFIG_KAISER */
+diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
+index aed2064..9284ec1 100644
+--- a/arch/x86/mm/kaslr.c
++++ b/arch/x86/mm/kaslr.c
+@@ -189,6 +189,6 @@ void __meminit init_trampoline(void)
+ 		*pud_tramp = *pud;
+ 	}
+ 
+-	set_pgd(&trampoline_pgd_entry,
+-		__pgd(_KERNPG_TABLE | __pa(pud_page_tramp)));
++	/* Avoid set_pgd(), in case it's complicated by CONFIG_KAISER */
++	trampoline_pgd_entry = __pgd(_KERNPG_TABLE | __pa(pud_page_tramp));
+ }
+-- 
+2.7.4
+