[RFC PATCH] arm64: don't vmap() invalid page

[Yury Norov]

vmap() takes struct page *pages as one of arguments, and user may provide
an invalid pointer, which would lead to DABT at address translation later.
Currently, kernel checks the pages against NULL. In my case, however, the
address was not NULL, and was big enough so that the hardware generated
Address Size Abort.

Interestingly, this abort happens even if copy_from_kernel_nofault() is used,
which is quite inconvenient for debugging purposes. 

This patch adds an arch_vmap_page_valid() helper into vmap() path, so that
architectures may add arch-specific checks of the pointer passed into vmap.

For arm64, if the page passed to vmap() corresponds to a physical address
greater than maximum possible value as described in TCR_EL1.IPS register, the
following table walk would generate Address Size Abort. Instead of creating
the invalid mapping, kernel will return ERANGE in such situation.

Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
---
 arch/arm64/include/asm/vmalloc.h | 41 ++++++++++++++++++++++++++++++++
 include/linux/vmalloc.h          |  7 ++++++
 mm/vmalloc.c                     |  8 +++++--
 3 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/vmalloc.h b/arch/arm64/include/asm/vmalloc.h
index b9185503feae..e9d43ee019ad 100644
--- a/arch/arm64/include/asm/vmalloc.h
+++ b/arch/arm64/include/asm/vmalloc.h
@@ -4,6 +4,47 @@
 #include <asm/page.h>
 #include <asm/pgtable.h>
 
+static inline u64 pa_size(u64 ips)
+{
+	switch (ips) {
+	case 0b000:
+		return 1UL << 32;
+	case 0b001:
+		return 1UL << 36;
+	case 0b010:
+		return 1UL << 40;
+	case 0b011:
+		return 1UL << 42;
+	case 0b100:
+		return 1UL << 44;
+	case 0b101:
+		return 1UL << 48;
+	case 0b110:
+		return 1UL << 52;
+	/* All other values */
+	default:
+		return 1UL << 52;
+	}
+}
+
+#define arch_vmap_page_valid arch_vmap_page_valid
+static inline int arch_vmap_page_valid(struct page *page)
+{
+	u64 tcr, ips, paddr_size;
+
+	if (!page)
+		return -ENOMEM;
+
+	tcr = read_sysreg_s(SYS_TCR_EL1);
+	ips = (tcr & TCR_IPS_MASK) >> TCR_IPS_SHIFT;
+
+	paddr_size = pa_size(ips);
+	if (page_to_phys(page) >= paddr_size)
+		return -ERANGE;
+
+	return 0;
+}
+
 #ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
 
 #define arch_vmap_pud_supported arch_vmap_pud_supported
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 6e022cc712e6..08b567d8bafc 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -119,6 +119,13 @@ static inline int arch_vmap_pte_supported_shift(unsigned long size)
 }
 #endif
 
+#ifndef arch_vmap_page_valid
+static inline int arch_vmap_page_valid(struct page *page)
+{
+	return page ? 0 : -ENOMEM;
+}
+#endif
+
 /*
  *	Highlevel APIs for driver use
  */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d2a00ad4e1dd..ee0384405cdd 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -472,11 +472,15 @@ static int vmap_pages_pte_range(pmd_t *pmd, unsigned long addr,
 		return -ENOMEM;
 	do {
 		struct page *page = pages[*nr];
+		int ret;
 
 		if (WARN_ON(!pte_none(*pte)))
 			return -EBUSY;
-		if (WARN_ON(!page))
-			return -ENOMEM;
+
+		ret = arch_vmap_page_valid(page);
+		if (WARN_ON(ret))
+			return ret;
+
 		set_pte_at(&init_mm, addr, pte, mk_pte(page, prot));
 		(*nr)++;
 	} while (pte++, addr += PAGE_SIZE, addr != end);
-- 
2.30.2