Re: FAILED: patch "[PATCH] arm64: hugetlb: avoid potential NULL dereference" failed to apply to 4.14-stable tree

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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