[mips] Correctly bounds check virt_addr_valid (Closes: #929366)

debian/changelog

@@ -20,6 +20,9 @@ linux (4.19.37-4) UNRELEASED; urgency=medium
     (CVE-2019-11833)
   * Bluetooth: hidp: fix buffer overflow (CVE-2019-11884)
 
+  [ Aurelien Jarno ]
+  * [mips] Correctly bounds check virt_addr_valid (Closes: #929366)
+
  -- Ben Hutchings <ben@decadent.org.uk>  Sun, 19 May 2019 00:04:16 +0100
 
 linux (4.19.37-3) unstable; urgency=medium

debian/patches/bugfix/mips/MIPS-Bounds-check-virt_addr_valid.patch

@@ -0,0 +1,75 @@
+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
+Origin: https://git.kernel.org/linus/074a1e1167afd82c26f6d03a9a8b997d564bb241
+
+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>
+---
+ arch/mips/mm/mmap.c | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
+index 2f616ebeb7e0..7755a1fad05a 100644
+--- a/arch/mips/mm/mmap.c
++++ b/arch/mips/mm/mmap.c
+@@ -203,6 +203,11 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
+ 
+ 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);
+-- 
+2.20.1
+

debian/patches/series

@@ -82,6 +82,7 @@ bugfix/arm64/arm64-dts-allwinner-a64-Enable-A64-timer-workaround.patch
 bugfix/mips/MIPS-Loongson-Introduce-and-use-loongson_llsc_mb.patch
 bugfix/powerpc/powerpc-vdso-make-vdso32-installation-conditional-in.patch
 bugfix/mips/MIPS-scall64-o32-Fix-indirect-syscall-number-load.patch
+bugfix/mips/MIPS-Bounds-check-virt_addr_valid.patch
 
 # Arch features
 features/mips/MIPS-increase-MAX-PHYSMEM-BITS-on-Loongson-3-only.patch