Re: [PATCH 4.19 24/25] uprobes: ensure that uprobe->offset and ->ref_ctr_offset are properly aligned

[Naresh Kamboju <naresh.kamboju@linaro.org>]

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

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