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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 v3 2/4] x86/xen: add basic KASAN support for PV kernel
Date:   Fri, 7 Feb 2020 14:26:50 +0000
Message-ID: <20200207142652.670-3-sergey.dyasli@citrix.com>
In-Reply-To: <20200207142652.670-1-sergey.dyasli@citrix.com>
References: <20200207142652.670-1-sergey.dyasli@citrix.com>
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Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Introduce and use xen_kasan_* functions that are needed to properly
initialise KASAN for Xen PV domains. Disable instrumentation for files
that are used by xen_start_kernel() before kasan_early_init() could
be called.

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>
---
v2 --> v3:
- Fix compilation without CONFIG_KASAN
- Dropped _pv prefixes from new functions
- Made xen_kasan_early_init() call kasan_map_early_shadow() directly
- Updated description

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 | 10 ++++++++-
 arch/x86/xen/Makefile       |  7 ++++++
 arch/x86/xen/enlighten_pv.c |  3 +++
 arch/x86/xen/mmu_pv.c       | 43 +++++++++++++++++++++++++++++++++++++
 drivers/xen/Makefile        |  2 ++
 include/linux/kasan.h       |  2 ++
 include/xen/xen-ops.h       | 10 +++++++++
 lib/Kconfig.kasan           |  3 ++-
 8 files changed, 78 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 763e71abc0fe..b862c03a2019 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -13,6 +13,8 @@
 #include <linux/sched/task.h>
 #include <linux/vmalloc.h>
 
+#include <xen/xen-ops.h>
+
 #include <asm/e820/types.h>
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
@@ -231,7 +233,7 @@ static void __init kasan_early_p4d_populate(pgd_t *pgd,
 	} while (p4d++, addr = next, addr != end && p4d_none(*p4d));
 }
 
-static void __init kasan_map_early_shadow(pgd_t *pgd)
+void __init kasan_map_early_shadow(pgd_t *pgd)
 {
 	/* See comment in kasan_init() */
 	unsigned long addr = KASAN_SHADOW_START & PGDIR_MASK;
@@ -317,6 +319,8 @@ void __init kasan_early_init(void)
 
 	kasan_map_early_shadow(early_top_pgt);
 	kasan_map_early_shadow(init_top_pgt);
+
+	xen_kasan_early_init();
 }
 
 void __init kasan_init(void)
@@ -348,6 +352,8 @@ void __init kasan_init(void)
 				__pgd(__pa(tmp_p4d_table) | _KERNPG_TABLE));
 	}
 
+	xen_kasan_pin_pgd(early_top_pgt);
+
 	load_cr3(early_top_pgt);
 	__flush_tlb_all();
 
@@ -412,6 +418,8 @@ void __init kasan_init(void)
 	load_cr3(init_top_pgt);
 	__flush_tlb_all();
 
+	xen_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 bbba8b17829a..a9a47f0bf22e 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -1771,6 +1771,41 @@ static void __init set_page_prot(void *addr, pgprot_t prot)
 {
 	return set_page_prot_flags(addr, prot, UVMF_NONE);
 }
+
+#ifdef CONFIG_KASAN
+void __init xen_kasan_early_init(void)
+{
+	if (!xen_pv_domain())
+		return;
+
+	/* 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);
+
+	/* Add KASAN mappings into initial PV page tables */
+	kasan_map_early_shadow((pgd_t *)xen_start_info->pt_base);
+}
+
+void __init xen_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_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);
+}
+#endif /* ifdef CONFIG_KASAN */
+
 #ifdef CONFIG_X86_32
 static void __init xen_map_identity_early(pmd_t *pmd, unsigned long max_pfn)
 {
@@ -1943,6 +1978,14 @@ 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/linux/kasan.h b/include/linux/kasan.h
index 5cde9e7c2664..2ab644229217 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -20,6 +20,8 @@ extern pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD];
 extern pud_t kasan_early_shadow_pud[PTRS_PER_PUD];
 extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
 
+void kasan_map_early_shadow(pgd_t *pgd);
+
 int kasan_populate_early_shadow(const void *shadow_start,
 				const void *shadow_end);
 
diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index 095be1d66f31..f67f1f2d73c6 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_PREEMPTION */
 
+#if defined(CONFIG_XEN_PV) && defined(CONFIG_KASAN)
+void xen_kasan_early_init(void);
+void xen_kasan_pin_pgd(pgd_t *pgd);
+void xen_kasan_unpin_pgd(pgd_t *pgd);
+#else
+static inline void xen_kasan_early_init(void) { }
+static inline void xen_kasan_pin_pgd(pgd_t *pgd) { }
+static inline void xen_kasan_unpin_pgd(pgd_t *pgd) { }
+#endif /* if defined(CONFIG_XEN_PV) && defined(CONFIG_KASAN) */
+
 #endif /* INCLUDE_XEN_OPS_H */
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