On Wed, May 13, 2020 at 04:23:11PM +0530, Naresh Kamboju wrote:

On Tue, 12 May 2020 at 16:56, gregkh@linuxfoundation.org wrote:

...

The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 027d0c7101f50cf03aeea9eebf484afd4920c8d3 Mon Sep 17 00:00:00 2001 From: Mark Rutland mark.rutland@arm.com Date: Tue, 5 May 2020 13:59:30 +0100 Subject: [PATCH] arm64: hugetlb: avoid potential NULL dereference MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

The static analyzer in GCC 10 spotted that in huge_pte_alloc() we may pass a NULL pmdp into pte_alloc_map() when pmd_alloc() returns NULL:

| CC arch/arm64/mm/pageattr.o | CC arch/arm64/mm/hugetlbpage.o | from arch/arm64/mm/hugetlbpage.c:10: | arch/arm64/mm/hugetlbpage.c: In function ‘huge_pte_alloc’: | ./arch/arm64/include/asm/pgtable-types.h:28:24: warning: dereference of NULL ‘pmdp’ [CWE-690] [-Wanalyzer-null-dereference] | ./arch/arm64/include/asm/pgtable.h:436:26: note: in expansion of macro ‘pmd_val’ | arch/arm64/mm/hugetlbpage.c:242:10: note: in expansion of macro ‘pte_alloc_map’ | |arch/arm64/mm/hugetlbpage.c:232:10: | |./arch/arm64/include/asm/pgtable-types.h:28:24: | ./arch/arm64/include/asm/pgtable.h:436:26: note: in expansion of macro ‘pmd_val’ | arch/arm64/mm/hugetlbpage.c:242:10: note: in expansion of macro ‘pte_alloc_map’

This can only occur when the kernel cannot allocate a page, and so is unlikely to happen in practice before other systems start failing.

We can avoid this by bailing out if pmd_alloc() fails, as we do earlier in the function if pud_alloc() fails.

Fixes: 66b3923a1a0f ("arm64: hugetlb: add support for PTE contiguous bit") Signed-off-by: Mark Rutland mark.rutland@arm.com Reported-by: Kyrill Tkachov kyrylo.tkachov@arm.com Cc: stable@vger.kernel.org # 4.5.x- Cc: Will Deacon will@kernel.org Signed-off-by: Catalin Marinas catalin.marinas@arm.com

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c index bbeb6a5a6ba6..0be3355e3499 100644 --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -230,6 +230,8 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, ptep = (pte_t *)pudp; } else if (sz == (CONT_PTE_SIZE)) { pmdp = pmd_alloc(mm, pudp, addr);

•           if (!pmdp)
  

•                   return NULL;
  
            WARN_ON(addr & (sz - 1));
            /*
  

As per the subject this patch failed to apply on 4.14 FYI, on stable-rc 4.14 branch arm64 architecture build failed.

# make -sk KBUILD_BUILD_USER=TuxBuild -C/linux -j16 ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTCC=gcc CC="sccache aarch64-linux-gnu-gcc" O=build Image 70 # 71 ../arch/arm64/mm/hugetlbpage.c: In function ‘huge_pte_alloc’: 72 ../arch/arm64/mm/hugetlbpage.c:223:8: error: ‘pmdp’ undeclared (first use in this function); did you mean ‘pmd’? 73 223 | if (!pmdp) 74 | ^~~~ 75 | pmd 76 ../arch/arm64/mm/hugetlbpage.c:223:8: note: each undeclared identifier is reported only once for each function it appears in 77 make[2]: *** [../scripts/Makefile.build:326: arch/arm64/mm/hugetlbpage.o] Error 1

ref: https://gitlab.com/Linaro/lkft/kernel-runs/-/jobs/550145375

Now dropped from 4.9 and 4.14 trees, the backport was incorrect...

greg k-h