Messages in this thread | | | From | Nick Desaulniers <> | Date | Wed, 27 Jan 2021 09:40:38 -0800 | Subject | Re: [PATCH v2] lkdtm: fix memory copy size for WRITE_KERN |
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On Wed, Jan 27, 2021 at 3:05 AM Candle Sun <candlesea@gmail.com> wrote: > > From: Candle Sun <candle.sun@unisoc.com> > > Though do_overwritten() follows do_nothing() in source code, the final > memory address order is determined by compiler. We can't always assume
^ "by the compiler."
> address of do_overwritten() is bigger than do_nothing(). At least the > Clang we are using places do_overwritten() before do_nothing() in the > object. This causes the copy size in lkdtm_WRITE_KERN() is *really*
Hopefully nothing else gets placed in between the two, otherwise we're going to overwrite that, too.
> big and WRITE_KERN test on ARM32 arch will fail. > > Get absolute value of the address substraction for memcpy() size.
^ typo: subtraction
> > Signed-off-by: Candle Sun <candle.sun@unisoc.com> > --- > Changes in v2: > - Use abs() in place of address comparison. > --- > drivers/misc/lkdtm/perms.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c > index 2dede2ef658f..fbb7f4554054 100644 > --- a/drivers/misc/lkdtm/perms.c > +++ b/drivers/misc/lkdtm/perms.c > @@ -31,13 +31,13 @@ static unsigned long ro_after_init __ro_after_init = 0x55AA5500; > * This just returns to the caller. It is designed to be copied into > * non-executable memory regions. > */ > -static void do_nothing(void) > +static noinline void do_nothing(void) > { > return; > } > > /* Must immediately follow do_nothing for size calculuations to work out. */
^ This comment is now obsolete and should be removed together with this patch. That will also fix the typo in it.
> -static void do_overwritten(void) > +static noinline void do_overwritten(void) > { > pr_info("do_overwritten wasn't overwritten!\n"); > return; > @@ -113,7 +113,7 @@ void lkdtm_WRITE_KERN(void) > size_t size; > volatile unsigned char *ptr; > > - size = (unsigned long)do_overwritten - (unsigned long)do_nothing; > + size = (size_t)abs((uintptr_t)do_overwritten - (uintptr_t)do_nothing); > ptr = (unsigned char *)do_overwritten; > > pr_info("attempting bad %zu byte write at %px\n", size, ptr); > -- > 2.17.0 >
-- Thanks, ~Nick Desaulniers
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