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    SubjectRe: [PATCH 4.19 24/25] uprobes: ensure that uprobe->offset and ->ref_ctr_offset are properly aligned
    On Wed, Jun 10, 2020 at 12:25:56AM +0530, Naresh Kamboju wrote:
    > On Tue, 9 Jun 2020 at 23:35, Greg Kroah-Hartman
    > <gregkh@linuxfoundation.org> wrote:
    > >
    > > From: Oleg Nesterov <oleg@redhat.com>
    > >
    > > commit 013b2deba9a6b80ca02f4fafd7dedf875e9b4450 upstream.
    > >
    > > uprobe_write_opcode() must not cross page boundary; prepare_uprobe()
    > > relies on arch_uprobe_analyze_insn() which should validate "vaddr" but
    > > some architectures (csky, s390, and sparc) don't do this.
    > >
    > > We can remove the BUG_ON() check in prepare_uprobe() and validate the
    > > offset early in __uprobe_register(). The new IS_ALIGNED() check matches
    > > the alignment check in arch_prepare_kprobe() on supported architectures,
    > > so I think that all insns must be aligned to UPROBE_SWBP_INSN_SIZE.
    > >
    > > Another problem is __update_ref_ctr() which was wrong from the very
    > > beginning, it can read/write outside of kmap'ed page unless "vaddr" is
    > > aligned to sizeof(short), __uprobe_register() should check this too.
    > >
    > > Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
    > > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
    > > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    > > Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    > > Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
    > > Tested-by: Sven Schnelle <svens@linux.ibm.com>
    > > Cc: Steven Rostedt <rostedt@goodmis.org>
    > > Cc: stable@vger.kernel.org
    > > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    > > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > >
    > > ---
    > > kernel/events/uprobes.c | 16 ++++++++++++----
    > > 1 file changed, 12 insertions(+), 4 deletions(-)
    > >
    > > --- a/kernel/events/uprobes.c
    > > +++ b/kernel/events/uprobes.c
    > > @@ -612,10 +612,6 @@ static int prepare_uprobe(struct uprobe
    > > if (ret)
    > > goto out;
    > >
    > > - /* uprobe_write_opcode() assumes we don't cross page boundary */
    > > - BUG_ON((uprobe->offset & ~PAGE_MASK) +
    > > - UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
    > > -
    > > smp_wmb(); /* pairs with the smp_rmb() in handle_swbp() */
    > > set_bit(UPROBE_COPY_INSN, &uprobe->flags);
    > >
    > > @@ -911,6 +907,15 @@ static int __uprobe_register(struct inod
    > > if (offset > i_size_read(inode))
    > > return -EINVAL;
    > >
    > > + /*
    > > + * This ensures that copy_from_page(), copy_to_page() and
    > > + * __update_ref_ctr() can't cross page boundary.
    > > + */
    > > + if (!IS_ALIGNED(offset, UPROBE_SWBP_INSN_SIZE))
    > > + return -EINVAL;
    > > + if (!IS_ALIGNED(ref_ctr_offset, sizeof(short)))
    >
    > stable-rc 4.19 build failure for x86_64, i386 and arm.
    > make -sk KBUILD_BUILD_USER=TuxBuild -C/linux -j16 ARCH=x86 HOSTCC=gcc
    > CC="sccache gcc" O=build
    >
    > 75 #
    > 76 In file included from ../kernel/events/uprobes.c:25:
    > 77 ../kernel/events/uprobes.c: In function ‘__uprobe_register’:
    > 78 ../kernel/events/uprobes.c:916:18: error: ‘ref_ctr_offset’
    > undeclared (first use in this function); did you mean
    > ‘per_cpu_offset’?
    > 79 916 | if (!IS_ALIGNED(ref_ctr_offset, sizeof(short)))
    > 80 | ^~~~~~~~~~~~~~
    > 81 ../include/linux/kernel.h:62:30: note: in definition of macro ‘IS_ALIGNED’
    > 82 62 | #define IS_ALIGNED(x, a) (((x) & ((typeof(x))(a) - 1)) == 0)
    > 83 | ^
    > 84 ../kernel/events/uprobes.c:916:18: note: each undeclared identifier
    > is reported only once for each function it appears in
    > 85 916 | if (!IS_ALIGNED(ref_ctr_offset, sizeof(short)))
    > 86 | ^~~~~~~~~~~~~~
    > 87 ../include/linux/kernel.h:62:30: note: in definition of macro ‘IS_ALIGNED’
    > 88 62 | #define IS_ALIGNED(x, a) (((x) & ((typeof(x))(a) - 1)) == 0)
    > 89 | ^
    > 90 make[3]: *** [../scripts/Makefile.build:304: kernel/events/uprobes.o] Error 1
    >
    > --
    > Linaro LKFT
    > https://lkft.linaro.org

    Good catch, my builders just caught it too :(

    4.19, 4.14, 4.9, and 4.4 are all broken, I have a fix will test it and
    push out -rc2 for all of those with it in a bit, thanks.

    greg k-h

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