To ensure we take the actual address of a function in kernel text, use
__va_function. Otherwise, with CONFIG_CFI_CLANG, the compiler replaces
the address with a pointer to the CFI jump table, which is actually in
the module when compiled with CONFIG_LKDTM=m.
Signed-off-by: Sami Tolvanen <[email protected]>
Acked-by: Kees Cook <[email protected]>
---
drivers/misc/lkdtm/usercopy.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
index 109e8d4302c1..d173d6175c87 100644
--- a/drivers/misc/lkdtm/usercopy.c
+++ b/drivers/misc/lkdtm/usercopy.c
@@ -314,7 +314,7 @@ void lkdtm_USERCOPY_KERNEL(void)
pr_info("attempting bad copy_to_user from kernel text: %px\n",
vm_mmap);
- if (copy_to_user((void __user *)user_addr, vm_mmap,
+ if (copy_to_user((void __user *)user_addr, __va_function(vm_mmap),
unconst + PAGE_SIZE)) {
pr_warn("copy_to_user failed, but lacked Oops\n");
goto free_user;
--
2.31.0.291.g576ba9dcdaf-goog
On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <[email protected]> wrote:
>
> To ensure we take the actual address of a function in kernel text, use
> __va_function. Otherwise, with CONFIG_CFI_CLANG, the compiler replaces
> the address with a pointer to the CFI jump table, which is actually in
> the module when compiled with CONFIG_LKDTM=m.
Should patch 10 and 12 be reordered against one another? Otherwise it
looks like 12 defines __va_function while 10 uses it?
>
> Signed-off-by: Sami Tolvanen <[email protected]>
> Acked-by: Kees Cook <[email protected]>
> ---
> drivers/misc/lkdtm/usercopy.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
> index 109e8d4302c1..d173d6175c87 100644
> --- a/drivers/misc/lkdtm/usercopy.c
> +++ b/drivers/misc/lkdtm/usercopy.c
> @@ -314,7 +314,7 @@ void lkdtm_USERCOPY_KERNEL(void)
>
> pr_info("attempting bad copy_to_user from kernel text: %px\n",
> vm_mmap);
> - if (copy_to_user((void __user *)user_addr, vm_mmap,
> + if (copy_to_user((void __user *)user_addr, __va_function(vm_mmap),
> unconst + PAGE_SIZE)) {
> pr_warn("copy_to_user failed, but lacked Oops\n");
> goto free_user;
> --
> 2.31.0.291.g576ba9dcdaf-goog
>
--
Thanks,
~Nick Desaulniers
On Thu, Mar 18, 2021 at 11:43 AM Nick Desaulniers
<[email protected]> wrote:
>
> On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <[email protected]> wrote:
> >
> > To ensure we take the actual address of a function in kernel text, use
> > __va_function. Otherwise, with CONFIG_CFI_CLANG, the compiler replaces
> > the address with a pointer to the CFI jump table, which is actually in
> > the module when compiled with CONFIG_LKDTM=m.
>
> Should patch 10 and 12 be reordered against one another? Otherwise it
> looks like 12 defines __va_function while 10 uses it?
Ah, nvm patch 3 defines a generic version, I see.
>
>
> >
> > Signed-off-by: Sami Tolvanen <[email protected]>
> > Acked-by: Kees Cook <[email protected]>
> > ---
> > drivers/misc/lkdtm/usercopy.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/misc/lkdtm/usercopy.c b/drivers/misc/lkdtm/usercopy.c
> > index 109e8d4302c1..d173d6175c87 100644
> > --- a/drivers/misc/lkdtm/usercopy.c
> > +++ b/drivers/misc/lkdtm/usercopy.c
> > @@ -314,7 +314,7 @@ void lkdtm_USERCOPY_KERNEL(void)
> >
> > pr_info("attempting bad copy_to_user from kernel text: %px\n",
> > vm_mmap);
> > - if (copy_to_user((void __user *)user_addr, vm_mmap,
> > + if (copy_to_user((void __user *)user_addr, __va_function(vm_mmap),
> > unconst + PAGE_SIZE)) {
> > pr_warn("copy_to_user failed, but lacked Oops\n");
> > goto free_user;
> > --
> > 2.31.0.291.g576ba9dcdaf-goog
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers
--
Thanks,
~Nick Desaulniers