Messages in this thread | | | From | Candle Sun <> | Date | Thu, 28 Jan 2021 14:46:52 +0800 | Subject | Re: [PATCH v2] lkdtm: fix memory copy size for WRITE_KERN |
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On Thu, Jan 28, 2021 at 1:40 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > 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
Thanks Nick. I will clean the typo and the comment line in the next patch.
Regards, Candle
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