Linux 5.1.9

[thirdparty/kernel/stable-queue.git] / releases / 5.1.9 / mips-bounds-check-virt_addr_valid.patch

From 074a1e1167afd82c26f6d03a9a8b997d564bb241 Mon Sep 17 00:00:00 2001
From: Paul Burton <paul.burton@mips.com>
Date: Tue, 28 May 2019 17:05:03 +0000
Subject: MIPS: Bounds check virt_addr_valid
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Paul Burton <paul.burton@mips.com>

commit 074a1e1167afd82c26f6d03a9a8b997d564bb241 upstream.

The virt_addr_valid() function is meant to return true iff
virt_to_page() will return a valid struct page reference. This is true
iff the address provided is found within the unmapped address range
between PAGE_OFFSET & MAP_BASE, but we don't currently check for that
condition. Instead we simply mask the address to obtain what will be a
physical address if the virtual address is indeed in the desired range,
shift it to form a PFN & then call pfn_valid(). This can incorrectly
return true if called with a virtual address which, after masking,
happens to form a physical address corresponding to a valid PFN.

For example we may vmalloc an address in the kernel mapped region
starting a MAP_BASE & obtain the virtual address:

  addr = 0xc000000000002000

When masked by virt_to_phys(), which uses __pa() & in turn CPHYSADDR(),
we obtain the following (bogus) physical address:

  addr = 0x2000

In a common system with PHYS_OFFSET=0 this will correspond to a valid
struct page which should really be accessed by virtual address
PAGE_OFFSET+0x2000, causing virt_addr_valid() to incorrectly return 1
indicating that the original address corresponds to a struct page.

This is equivalent to the ARM64 change made in commit ca219452c6b8
("arm64: Correctly bounds check virt_addr_valid").

This fixes fallout when hardened usercopy is enabled caused by the
related commit 517e1fbeb65f ("mm/usercopy: Drop extra
is_vmalloc_or_module() check") which removed a check for the vmalloc
range that was present from the introduction of the hardened usercopy
feature.

Signed-off-by: Paul Burton <paul.burton@mips.com>
References: ca219452c6b8 ("arm64: Correctly bounds check virt_addr_valid")
References: 517e1fbeb65f ("mm/usercopy: Drop extra is_vmalloc_or_module() check")
Reported-by: Julien Cristau <jcristau@debian.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: YunQiang Su <ysu@wavecomp.com>
URL: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=929366
Cc: stable@vger.kernel.org # v4.12+
Cc: linux-mips@vger.kernel.org
Cc: Yunqiang Su <ysu@wavecomp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/mips/mm/mmap.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/mips/mm/mmap.c
+++ b/arch/mips/mm/mmap.c
@@ -203,6 +203,11 @@ unsigned long arch_randomize_brk(struct
 
 int __virt_addr_valid(const volatile void *kaddr)
 {
+	unsigned long vaddr = (unsigned long)vaddr;
+
+	if ((vaddr < PAGE_OFFSET) || (vaddr >= MAP_BASE))
+		return 0;
+
 	return pfn_valid(PFN_DOWN(virt_to_phys(kaddr)));
 }
 EXPORT_SYMBOL_GPL(__virt_addr_valid);