Messages in this thread | | | Subject | Re: [PATCH v1 08/10] lkdtm: Really write into kernel text in WRITE_KERN | From | Christophe Leroy <> | Date | Wed, 13 Oct 2021 09:29:53 +0200 |
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Le 13/10/2021 à 09:05, Kees Cook a écrit : > On Mon, Oct 11, 2021 at 05:25:35PM +0200, Christophe Leroy wrote: >> WRITE_KERN is supposed to overwrite some kernel text, namely >> do_overwritten() function. >> >> But at the time being it overwrites do_overwritten() function >> descriptor, not function text. >> >> Fix it by dereferencing the function descriptor to obtain >> function text pointer. >> >> And make do_overwritten() noinline so that it is really >> do_overwritten() which is called by lkdtm_WRITE_KERN(). >> >> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> >> --- >> drivers/misc/lkdtm/perms.c | 8 +++++--- >> 1 file changed, 5 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c >> index 60b3b2fe929d..442d60ed25ef 100644 >> --- a/drivers/misc/lkdtm/perms.c >> +++ b/drivers/misc/lkdtm/perms.c >> @@ -5,6 +5,7 @@ >> * even non-readable regions. >> */ >> #include "lkdtm.h" >> +#include <linux/kallsyms.h> > > Why not #include <asm/sections.h> instead here?
dereference_symbol_descriptor() is defined in linux/kallsyms.h
> >> #include <linux/slab.h> >> #include <linux/vmalloc.h> >> #include <linux/mman.h> >> @@ -37,7 +38,7 @@ static noinline void do_nothing(void) >> } >> >> /* Must immediately follow do_nothing for size calculuations to work out. */ >> -static void do_overwritten(void) >> +static noinline void do_overwritten(void) >> { >> pr_info("do_overwritten wasn't overwritten!\n"); >> return; >> @@ -113,8 +114,9 @@ void lkdtm_WRITE_KERN(void) >> size_t size; >> volatile unsigned char *ptr; >> >> - size = (unsigned long)do_overwritten - (unsigned long)do_nothing; >> - ptr = (unsigned char *)do_overwritten; >> + size = (unsigned long)dereference_symbol_descriptor(do_overwritten) - >> + (unsigned long)dereference_symbol_descriptor(do_nothing); >> + ptr = dereference_symbol_descriptor(do_overwritten); > > But otherwise, yup, I expect there will be a bunch of things like this > to clean up in LKDTM. :| Sorry about that! > > Acked-by: Kees Cook <keescook@chromium.org> > >> >> pr_info("attempting bad %zu byte write at %px\n", size, ptr); >> memcpy((void *)ptr, (unsigned char *)do_nothing, size); >> -- >> 2.31.1 >> >
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