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From:   Sergey Dyasli <sergey.dyasli@citrix.com>
To:     <xen-devel@lists.xen.org>, <kasan-dev@googlegroups.com>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
CC:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        "Stefano Stabellini" <sstabellini@kernel.org>,
        George Dunlap <george.dunlap@citrix.com>,
        Ross Lagerwall <ross.lagerwall@citrix.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sergey Dyasli <sergey.dyasli@citrix.com>
Subject: [PATCH v2 2/4] x86/xen: add basic KASAN support for PV kernel
Date:   Fri, 17 Jan 2020 12:58:32 +0000
Message-ID: <20200117125834.14552-3-sergey.dyasli@citrix.com>
In-Reply-To: <20200117125834.14552-1-sergey.dyasli@citrix.com>
References: <20200117125834.14552-1-sergey.dyasli@citrix.com>
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Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

This enables to use Outline instrumentation for Xen PV kernels.

KASAN_INLINE and KASAN_VMALLOC options currently lead to boot crashes
and hence disabled.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
---
v1 --> v2:
- Fix compilation without CONFIG_XEN_PV
- Use macros for KASAN_SHADOW_START

RFC --> v1:
- New functions with declarations in xen/xen-ops.h
- Fixed the issue with free_kernel_image_pages() with the help of
  xen_pv_kasan_unpin_pgd()
---
 arch/x86/mm/kasan_init_64.c | 12 ++++++++++++
 arch/x86/xen/Makefile       |  7 +++++++
 arch/x86/xen/enlighten_pv.c |  3 +++
 arch/x86/xen/mmu_pv.c       | 38 +++++++++++++++++++++++++++++++++++++
 drivers/xen/Makefile        |  2 ++
 include/xen/xen-ops.h       | 10 ++++++++++
 kernel/Makefile             |  2 ++
 lib/Kconfig.kasan           |  3 ++-
 8 files changed, 76 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index cf5bc37c90ac..902a6a152d33 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -13,6 +13,9 @@
 #include <linux/sched/task.h>
 #include <linux/vmalloc.h>
 
+#include <xen/xen.h>
+#include <xen/xen-ops.h>
+
 #include <asm/e820/types.h>
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
@@ -332,6 +335,11 @@ void __init kasan_early_init(void)
 	for (i = 0; pgtable_l5_enabled() && i < PTRS_PER_P4D; i++)
 		kasan_early_shadow_p4d[i] = __p4d(p4d_val);
 
+	if (xen_pv_domain()) {
+		pgd_t *pv_top_pgt = xen_pv_kasan_early_init();
+		kasan_map_early_shadow(pv_top_pgt);
+	}
+
 	kasan_map_early_shadow(early_top_pgt);
 	kasan_map_early_shadow(init_top_pgt);
 }
@@ -369,6 +377,8 @@ void __init kasan_init(void)
 				__pgd(__pa(tmp_p4d_table) | _KERNPG_TABLE));
 	}
 
+	xen_pv_kasan_pin_pgd(early_top_pgt);
+
 	load_cr3(early_top_pgt);
 	__flush_tlb_all();
 
@@ -433,6 +443,8 @@ void __init kasan_init(void)
 	load_cr3(init_top_pgt);
 	__flush_tlb_all();
 
+	xen_pv_kasan_unpin_pgd(early_top_pgt);
+
 	/*
 	 * kasan_early_shadow_page has been used as early shadow memory, thus
 	 * it may contain some garbage. Now we can clear and write protect it,
diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile
index 084de77a109e..102fad0b0bca 100644
--- a/arch/x86/xen/Makefile
+++ b/arch/x86/xen/Makefile
@@ -1,3 +1,10 @@
+KASAN_SANITIZE_enlighten_pv.o := n
+KASAN_SANITIZE_enlighten.o := n
+KASAN_SANITIZE_irq.o := n
+KASAN_SANITIZE_mmu_pv.o := n
+KASAN_SANITIZE_p2m.o := n
+KASAN_SANITIZE_multicalls.o := n
+
 # SPDX-License-Identifier: GPL-2.0
 OBJECT_FILES_NON_STANDARD_xen-asm_$(BITS).o := y
 
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index ae4a41ca19f6..27de55699f24 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -72,6 +72,7 @@
 #include <asm/mwait.h>
 #include <asm/pci_x86.h>
 #include <asm/cpu.h>
+#include <asm/kasan.h>
 
 #ifdef CONFIG_ACPI
 #include <linux/acpi.h>
@@ -1231,6 +1232,8 @@ asmlinkage __visible void __init xen_start_kernel(void)
 	/* Get mfn list */
 	xen_build_dynamic_phys_to_machine();
 
+	kasan_early_init();
+
 	/*
 	 * Set up kernel GDT and segment registers, mainly so that
 	 * -fstack-protector code can be executed.
diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index c8dbee62ec2a..5cd63e37a2db 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -1771,6 +1771,36 @@ static void __init set_page_prot(void *addr, pgprot_t prot)
 {
 	return set_page_prot_flags(addr, prot, UVMF_NONE);
 }
+
+pgd_t * __init xen_pv_kasan_early_init(void)
+{
+	/* PV page tables must be read-only */
+	set_page_prot(kasan_early_shadow_pud, PAGE_KERNEL_RO);
+	set_page_prot(kasan_early_shadow_pmd, PAGE_KERNEL_RO);
+	set_page_prot(kasan_early_shadow_pte, PAGE_KERNEL_RO);
+
+	/* Return a pointer to the initial PV page tables */
+	return (pgd_t *)xen_start_info->pt_base;
+}
+
+void __init xen_pv_kasan_pin_pgd(pgd_t *pgd)
+{
+	if (!xen_pv_domain())
+		return;
+
+	set_page_prot(pgd, PAGE_KERNEL_RO);
+	pin_pagetable_pfn(MMUEXT_PIN_L4_TABLE, PFN_DOWN(__pa_symbol(pgd)));
+}
+
+void __init xen_pv_kasan_unpin_pgd(pgd_t *pgd)
+{
+	if (!xen_pv_domain())
+		return;
+
+	pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa_symbol(pgd)));
+	set_page_prot(pgd, PAGE_KERNEL);
+}
+
 #ifdef CONFIG_X86_32
 static void __init xen_map_identity_early(pmd_t *pmd, unsigned long max_pfn)
 {
@@ -1943,6 +1973,14 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
 	if (i && i < pgd_index(__START_KERNEL_map))
 		init_top_pgt[i] = ((pgd_t *)xen_start_info->pt_base)[i];
 
+#ifdef CONFIG_KASAN
+	/* Copy KASAN mappings */
+	for (i = pgd_index(KASAN_SHADOW_START);
+	     i < pgd_index(KASAN_SHADOW_END);
+	     i++)
+		init_top_pgt[i] = ((pgd_t *)xen_start_info->pt_base)[i];
+#endif /* ifdef CONFIG_KASAN */
+
 	/* Make pagetable pieces RO */
 	set_page_prot(init_top_pgt, PAGE_KERNEL_RO);
 	set_page_prot(level3_ident_pgt, PAGE_KERNEL_RO);
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 0c4efa6fe450..1e9e1e41c0a8 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -1,4 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
+KASAN_SANITIZE_features.o := n
+
 obj-$(CONFIG_HOTPLUG_CPU)		+= cpu_hotplug.o
 obj-y	+= grant-table.o features.o balloon.o manage.o preempt.o time.o
 obj-y	+= mem-reservation.o
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index d89969aa9942..3d20f000af12 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -241,4 +241,14 @@ static inline void xen_preemptible_hcall_end(void)
 
 #endif /* CONFIG_PREEMPT */
 
+#if defined(CONFIG_XEN_PV)
+pgd_t *xen_pv_kasan_early_init(void);
+void xen_pv_kasan_pin_pgd(pgd_t *pgd);
+void xen_pv_kasan_unpin_pgd(pgd_t *pgd);
+#else
+static inline pgd_t *xen_pv_kasan_early_init(void) { return NULL; }
+static inline void xen_pv_kasan_pin_pgd(pgd_t *pgd) { }
+static inline void xen_pv_kasan_unpin_pgd(pgd_t *pgd) { }
+#endif /* defined(CONFIG_XEN_PV) */
+
 #endif /* INCLUDE_XEN_OPS_H */
diff --git a/kernel/Makefile b/kernel/Makefile
index f2cc0d118a0b..1da6fd93c00c 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -12,6 +12,8 @@ obj-y     = fork.o exec_domain.o panic.o \
 	    notifier.o ksysfs.o cred.o reboot.o \
 	    async.o range.o smpboot.o ucount.o
 
+KASAN_SANITIZE_cpu.o := n
+
 obj-$(CONFIG_MODULES) += kmod.o
 obj-$(CONFIG_MULTIUSER) += groups.o
 
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index 81f5464ea9e1..429a638625ea 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -98,6 +98,7 @@ config KASAN_OUTLINE
 
 config KASAN_INLINE
 	bool "Inline instrumentation"
+	depends on !XEN_PV
 	help
 	  Compiler directly inserts code checking shadow memory before
 	  memory accesses. This is faster than outline (in some workloads
@@ -147,7 +148,7 @@ config KASAN_SW_TAGS_IDENTIFY
 
 config KASAN_VMALLOC
 	bool "Back mappings in vmalloc space with real shadow memory"
-	depends on KASAN && HAVE_ARCH_KASAN_VMALLOC
+	depends on KASAN && HAVE_ARCH_KASAN_VMALLOC && !XEN_PV
 	help
 	  By default, the shadow region for vmalloc space is the read-only
 	  zero page. This means that KASAN cannot detect errors involving
-- 
2.17.1