| Message ID | 44946ed0340013a52f8acdee7d6d0781f145cd6b.1634190022.git.christophe.leroy@csgroup.eu (mailing list archive) |
|---|---|
| State | Awaiting Upstream, archived |
| Headers | show |
| Series | Fix LKDTM for PPC64/IA64/PARISC | expand |
On Thu, Oct 14, 2021 at 07:50:00AM +0200, Christophe Leroy wrote: > Behind its location, lkdtm_EXEC_RODATA() executes > lkdtm_rodata_do_nothing() which is a real function, > not a copy of do_nothing(). > > So executes it directly instead of using execute_location(). > > This is necessary because following patch will fix execute_location() > to use a copy of the function descriptor of do_nothing() and > function descriptor of lkdtm_rodata_do_nothing() might be different. > > And fix displayed addresses by dereferencing the function descriptors. > > Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> I still don't understand this -- it doesn't look needed at all given the changes in patch 12. (i.e. everything is using dereference_function_descriptor() now) Can't this patch be dropped? -Kees > --- > drivers/misc/lkdtm/perms.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c > index 035fcca441f0..5266dc28df6e 100644 > --- a/drivers/misc/lkdtm/perms.c > +++ b/drivers/misc/lkdtm/perms.c > @@ -153,7 +153,14 @@ void lkdtm_EXEC_VMALLOC(void) > > void lkdtm_EXEC_RODATA(void) > { > - execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS); > + pr_info("attempting ok execution at %px\n", > + dereference_function_descriptor(do_nothing)); > + do_nothing(); > + > + pr_info("attempting bad execution at %px\n", > + dereference_function_descriptor(lkdtm_rodata_do_nothing)); > + lkdtm_rodata_do_nothing(); > + pr_err("FAIL: func returned\n"); > } > > void lkdtm_EXEC_USERSPACE(void) > -- > 2.31.1 >
Le 15/10/2021 à 23:32, Kees Cook a écrit : > On Thu, Oct 14, 2021 at 07:50:00AM +0200, Christophe Leroy wrote: >> Behind its location, lkdtm_EXEC_RODATA() executes >> lkdtm_rodata_do_nothing() which is a real function, >> not a copy of do_nothing(). >> >> So executes it directly instead of using execute_location(). >> >> This is necessary because following patch will fix execute_location() >> to use a copy of the function descriptor of do_nothing() and >> function descriptor of lkdtm_rodata_do_nothing() might be different. >> >> And fix displayed addresses by dereferencing the function descriptors. >> >> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> > > I still don't understand this -- it doesn't look needed at all given the > changes in patch 12. (i.e. everything is using > dereference_function_descriptor() now) dereference_function_descriptor() only deals with the function address, not the function TOC. do_nothing() is a function. It has a function descriptor with a given address (address of .do_nothing) and a given TOC, say TOC1. lkdtm_rodata_do_nothing() is another function. It has its own function descriptor with a given address (address of .lkdtm_rodata_do_nothing) and a given TOC, say TOC2. If we use execute_location(), it will copy do_nothing() function descriptor and change the function address to the address of lkdtm_rodata_do_nothing(). So it will call lkdtm_rodata_do_nothing() with TOC1 instead of calling it with TOC2. > > Can't this patch be dropped? It is likely that the TOC will be the same for both functions, and anyway those functions are so simple that they don't use the TOC at all, so yes it would likely work without this patch but from my point of view it is incorrect to call one function with the TOC from the descriptor of another function. If you thing we can take the risk, then I'm happy to drop the patch and replace it by execute_location(dereference_function_descriptor(lkdtm_rodata_do_nothing), CODE_AS_IS) Christophe
Le 16/10/2021 à 08:41, Christophe Leroy a écrit : > > > Le 15/10/2021 à 23:32, Kees Cook a écrit : >> On Thu, Oct 14, 2021 at 07:50:00AM +0200, Christophe Leroy wrote: >>> Behind its location, lkdtm_EXEC_RODATA() executes >>> lkdtm_rodata_do_nothing() which is a real function, >>> not a copy of do_nothing(). >>> >>> So executes it directly instead of using execute_location(). >>> >>> This is necessary because following patch will fix execute_location() >>> to use a copy of the function descriptor of do_nothing() and >>> function descriptor of lkdtm_rodata_do_nothing() might be different. >>> >>> And fix displayed addresses by dereferencing the function descriptors. >>> >>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> >> >> I still don't understand this -- it doesn't look needed at all given the >> changes in patch 12. (i.e. everything is using >> dereference_function_descriptor() now) > > dereference_function_descriptor() only deals with the function address, > not the function TOC. > > do_nothing() is a function. It has a function descriptor with a given > address (address of .do_nothing) and a given TOC, say TOC1. > > lkdtm_rodata_do_nothing() is another function. It has its own function > descriptor with a given address (address of .lkdtm_rodata_do_nothing) > and a given TOC, say TOC2. > > If we use execute_location(), it will copy do_nothing() function > descriptor and change the function address to the address of > lkdtm_rodata_do_nothing(). So it will call lkdtm_rodata_do_nothing() > with TOC1 instead of calling it with TOC2. > >> >> Can't this patch be dropped? > > It is likely that the TOC will be the same for both functions, and > anyway those functions are so simple that they don't use the TOC at all, > so yes it would likely work without this patch but from my point of view > it is incorrect to call one function with the TOC from the descriptor of > another function. > > If you thing we can take the risk, then I'm happy to drop the patch and > replace it by > > execute_location(dereference_function_descriptor(lkdtm_rodata_do_nothing), CODE_AS_IS) > Once we have patch 12 EXEC_RODATA works well on powerpc without this patch so I will drop this patch for now and will propose something else as a follow-up to my series. Christophe
diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c index 035fcca441f0..5266dc28df6e 100644 --- a/drivers/misc/lkdtm/perms.c +++ b/drivers/misc/lkdtm/perms.c @@ -153,7 +153,14 @@ void lkdtm_EXEC_VMALLOC(void) void lkdtm_EXEC_RODATA(void) { - execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS); + pr_info("attempting ok execution at %px\n", + dereference_function_descriptor(do_nothing)); + do_nothing(); + + pr_info("attempting bad execution at %px\n", + dereference_function_descriptor(lkdtm_rodata_do_nothing)); + lkdtm_rodata_do_nothing(); + pr_err("FAIL: func returned\n"); } void lkdtm_EXEC_USERSPACE(void)
Behind its location, lkdtm_EXEC_RODATA() executes lkdtm_rodata_do_nothing() which is a real function, not a copy of do_nothing(). So executes it directly instead of using execute_location(). This is necessary because following patch will fix execute_location() to use a copy of the function descriptor of do_nothing() and function descriptor of lkdtm_rodata_do_nothing() might be different. And fix displayed addresses by dereferencing the function descriptors. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> --- drivers/misc/lkdtm/perms.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)