[PATCH] arm64: kasan: fix phys_to_virt() false positive on tag-based kasan

[Walter Wu]

__arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
but it will modify pointer tag into 0xff, so there is a false positive.

When enable tag-based kasan, phys_to_virt() function need to rewrite
its original pointer tag in order to avoid kasan report an incorrect
memory corruption.

BUG: KASAN: double-free or invalid-free in __arm_v7s_unmap+0x720/0xda4
Pointer tag: [ff], memory tag: [c1]

Call trace:
 dump_backtrace+0x0/0x1d4
 show_stack+0x14/0x1c
 dump_stack+0xe8/0x140
 print_address_description+0x80/0x2f0
 kasan_report_invalid_free+0x58/0x74
 __kasan_slab_free+0x1e4/0x220
 kasan_slab_free+0xc/0x18
 kmem_cache_free+0xfc/0x884
 __arm_v7s_unmap+0x720/0xda4
 __arm_v7s_map+0xc8/0x774
 arm_v7s_map+0x80/0x158
 mtk_iommu_map+0xb4/0xe0
 iommu_map+0x154/0x450
 iommu_map_sg+0xe4/0x150
 iommu_dma_map_sg+0x214/0x4ec
 __iommu_map_sg_attrs+0xf0/0x110
 ion_map_dma_buf+0xe8/0x114
 dma_buf_map_attachment+0x4c/0x80
 disp_sync_prepare_buf+0x378/0x820
 _ioctl_prepare_buffer+0x130/0x870
 mtk_disp_mgr_ioctl+0x5c4/0xab0
 do_vfs_ioctl+0x8e0/0x15a4
 __arm64_sys_ioctl+0x8c/0xb4
 el0_svc_common+0xe4/0x1e0
 el0_svc_handler+0x30/0x3c
 el0_svc+0x8/0xc

Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
---
 arch/arm64/include/asm/kasan.h  |  1 -
 arch/arm64/include/asm/memory.h | 10 ++++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kasan.h b/arch/arm64/include/asm/kasan.h
index b52aacd2c526..59894cafad60 100644
--- a/arch/arm64/include/asm/kasan.h
+++ b/arch/arm64/include/asm/kasan.h
@@ -5,7 +5,6 @@
 #ifndef __ASSEMBLY__
 
 #include <linux/linkage.h>
-#include <asm/memory.h>
 #include <asm/pgtable-types.h>
 
 #define arch_kasan_set_tag(addr, tag)	__tag_set(addr, tag)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 8ffcf5a512bb..75af5ba9ff22 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -171,6 +171,7 @@
 
 #include <linux/bitops.h>
 #include <linux/mmdebug.h>
+#include <asm/kasan.h>
 
 extern s64			memstart_addr;
 /* PHYS_OFFSET - the physical address of the start of memory. */
@@ -282,7 +283,16 @@ static inline phys_addr_t virt_to_phys(const volatile void *x)
 #define phys_to_virt phys_to_virt
 static inline void *phys_to_virt(phys_addr_t x)
 {
+#ifdef CONFIG_KASAN_SW_TAGS
+	unsigned long addr = __phys_to_virt(x);
+	u8 *tag = (void *)(addr >> KASAN_SHADOW_SCALE_SHIFT)
+				+ KASAN_SHADOW_OFFSET;
+
+	addr = __tag_set(addr, *tag);
+	return (void *)addr;
+#else
 	return (void *)(__phys_to_virt(x));
+#endif
 }
 
 /*
-- 
2.18.0