From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [103.22.144.67]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3sQctl4JQkzDrfR for ; Fri, 2 Sep 2016 21:52:31 +1000 (AEST) Date: Fri, 2 Sep 2016 21:47:59 +1000 From: Paul Mackerras To: linuxppc-dev@lists.ozlabs.org Cc: "Aneesh Kumar K.V" Subject: [PATCH 1/3] powerpc/mm: Don't alias user region to other regions below PAGE_OFFSET Message-ID: <20160902114759.GA12433@fergus.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , In commit c60ac5693c47 ("powerpc: Update kernel VSID range", 2013-03-13) we lost a check on the region number (the top four bits of the effective address) for addresses below PAGE_OFFSET. That commit replaced a check that the top 18 bits were all zero with a check that bits 46 - 59 were zero (performed for all addresses, not just user addresses). This means that userspace can access an address like 0x1000_0xxx_xxxx_xxxx and we will insert a valid SLB entry for it. The VSID used will be the same as if the top 4 bits were 0, but the page size will be some random value obtained by indexing beyond the end of the mm_ctx_high_slices_psize array in the paca. If that page size is the same as would be used for region 0, then userspace just has an alias of the region 0 space. If the page size is different, then no HPTE will be found for the access, and the process will get a SIGSEGV (since hash_page_mm() will refuse to create a HPTE for the bogus address). The access beyond the end of the mm_ctx_high_slices_psize can be at most 5.5MB past the array, and so will be in RAM somewhere. Since the access is a load performed in real mode, it won't fault or crash the kernel. At most this bug could perhaps leak a little bit of information about blocks of 32 bytes of memory located at offsets of i * 512kB past the paca->mm_ctx_high_slices_psize array, for 1 <= i <= 11. Cc: stable@vger.kernel.org # v3.10+ Cc: Aneesh Kumar K.V Signed-off-by: Paul Mackerras --- arch/powerpc/mm/slb_low.S | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/mm/slb_low.S b/arch/powerpc/mm/slb_low.S index dfdb90c..9f19834 100644 --- a/arch/powerpc/mm/slb_low.S +++ b/arch/powerpc/mm/slb_low.S @@ -113,7 +113,12 @@ BEGIN_FTR_SECTION END_MMU_FTR_SECTION_IFCLR(MMU_FTR_1T_SEGMENT) b slb_finish_load_1T -0: +0: /* + * For userspace addresses, make sure this is region 0. + */ + cmpdi r9, 0 + bne 8f + /* when using slices, we extract the psize off the slice bitmaps * and then we need to get the sllp encoding off the mmu_psize_defs * array. -- 2.7.4