[PATCH] arm64: Add translation functions for /dev/mem read/write

[Sameer Goel]

Port architecture specific xlate and unxlate functions for /dev/mem
read/write. This sets up the mapping for a valid physical address if a
kernel direct mapping is not already present.

This is a generic issue as a user space app should not be allowed to crash
the kernel. This issue was observed when systemd tried to access performance
pointer record from the FPDT table.

Ported from commit e045fb2a988a ("x86: PAT avoid aliasing in /dev/mem
read/write")

Crash Signature:
 Unable to handle kernel paging request at virtual address ffff800008ff0000
 pgd = ffff8007de8b2200
 [ffff800008ff0000] *pgd=0000000000000000, *pud=0000000000000000
 Internal error: Oops: 96000007 [#1] SMP
................
 CPU: 0 PID: 1 Comm: systemd Not tainted 4.10.0 #1
 task: ffff8007c0820000 task.stack: ffff8007c0900000
 PC is at __arch_copy_to_user+0xb4/0x280
 LR is at read_mem+0xc0/0x138
 pc : [<ffff0000084b3bb4>] lr : [<ffff00000869d178>]
pstate: 80000145
 sp : ffff8007c0903d40
....................
 x3 : ffff800800000000 x2 : 0000000000000008
 x1 : ffff800008ff0000 x0 : 0000fffff6fdac00
....................
 Call trace:
 Exception stack(0xffff8007c0903b70 to 0xffff8007c0903ca0)
 [<ffff0000084b3bb4>] __arch_copy_to_user+0xb4/0x280
 [<ffff0000082454d0>] __vfs_read+0x48/0x130
 [<ffff0000082467dc>] vfs_read+0x8c/0x148
 [<ffff000008247a34>] SyS_pread64+0x94/0xa8
 [<ffff0000080833b0>] el0_svc_naked+0x24/0x28
 Code: a88120c7 d503201f d503201f 36180082 (f8408423)

Signed-off-by: Sameer Goel <sgoel@xxxxxxxxxxxxxx>
Tested-by: Shanker Donthineni <shankerd@xxxxxxxxxxxxxx>
---
 arch/arm64/include/asm/io.h |  5 +++++
 arch/arm64/mm/ioremap.c     | 31 +++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
index 0c00c87..c869ea4 100644
--- a/arch/arm64/include/asm/io.h
+++ b/arch/arm64/include/asm/io.h
@@ -183,6 +183,11 @@ static inline u64 __raw_readq(const volatile void __iomem *addr)
 #define iowrite32be(v,p)	({ __iowmb(); __raw_writel((__force __u32)cpu_to_be32(v), p); })
 #define iowrite64be(v,p)	({ __iowmb(); __raw_writeq((__force __u64)cpu_to_be64(v), p); })
 
+extern void *xlate_dev_mem_ptr(phys_addr_t phys);
+extern void unxlate_dev_mem_ptr(phys_addr_t phys, void *addr);
+
+#define xlate_dev_mem_ptr xlate_dev_mem_ptr
+#define unxlate_dev_mem_ptr unxlate_dev_mem_ptr
 #include <asm-generic/io.h>
 
 /*
diff --git a/arch/arm64/mm/ioremap.c b/arch/arm64/mm/ioremap.c
index c4c8cd4..ba7e63b 100644
--- a/arch/arm64/mm/ioremap.c
+++ b/arch/arm64/mm/ioremap.c
@@ -24,6 +24,7 @@
 #include <linux/mm.h>
 #include <linux/vmalloc.h>
 #include <linux/io.h>
+#include <linux/memblock.h>
 
 #include <asm/fixmap.h>
 #include <asm/tlbflush.h>
@@ -105,6 +106,36 @@ void __iomem *ioremap_cache(phys_addr_t phys_addr, size_t size)
 EXPORT_SYMBOL(ioremap_cache);
 
 /*
+ * Convert a physical pointer to a virtual kernel pointer for /dev/mem
+ * access
+ */
+void *xlate_dev_mem_ptr(phys_addr_t phys)
+{
+	unsigned long start  = phys &  PAGE_MASK;
+	unsigned long offset = phys & ~PAGE_MASK;
+	void *vaddr;
+
+	/* If page is RAM, we can use __va. Otherwise ioremap and unmap. */
+	if (page_is_ram(start >> PAGE_SHIFT) && memblock_is_memory(phys))
+		return __va(phys);
+
+	vaddr = ioremap_cache(start, PAGE_SIZE);
+	 /* Add the offset on success and return NULL if ioremap() failed */
+	if (vaddr)
+		vaddr += offset;
+
+	return vaddr;
+}
+
+void unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
+{
+	if (page_is_ram(phys >> PAGE_SHIFT))
+		return;
+
+	iounmap((void __iomem *)((unsigned long)addr & PAGE_MASK));
+}
+
+/*
  * Must be called after early_fixmap_init
  */
 void __init early_ioremap_init(void)
-- 
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