Re: [PATCH v4 04/45] x86: asm: instrument usercopy in get_user() and __put_user_size()

[Marco Elver]

On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@xxxxxxxxxx> wrote:
>
> Use hooks from instrumented.h to notify bug detection tools about
> usercopy events in get_user() and put_user_size().
>
> It's still unclear how to instrument put_user(), which assumes that
> instrumentation code doesn't clobber RAX.

do_put_user_call() has a comment about KASAN clobbering %ax, doesn't
this also apply to KMSAN? If not, could we have a <asm/instrumented.h>
that provides helpers to push registers on the stack and pop them back
on return?

Also it seems the test robot complained about this patch.

> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> ---
> Link: https://linux-review.googlesource.com/id/Ia9f12bfe5832623250e20f1859fdf5cc485a2fce
> ---
>  arch/x86/include/asm/uaccess.h | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 913e593a3b45f..1a8b5a234474f 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -5,6 +5,7 @@
>   * User space memory access functions
>   */
>  #include <linux/compiler.h>
> +#include <linux/instrumented.h>
>  #include <linux/kasan-checks.h>
>  #include <linux/string.h>
>  #include <asm/asm.h>
> @@ -99,11 +100,13 @@ extern int __get_user_bad(void);
>         int __ret_gu;                                                   \
>         register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX);            \
>         __chk_user_ptr(ptr);                                            \
> +       instrument_copy_from_user_before((void *)&(x), ptr, sizeof(*(ptr))); \
>         asm volatile("call __" #fn "_%P4"                               \
>                      : "=a" (__ret_gu), "=r" (__val_gu),                \
>                         ASM_CALL_CONSTRAINT                             \
>                      : "0" (ptr), "i" (sizeof(*(ptr))));                \
>         (x) = (__force __typeof__(*(ptr))) __val_gu;                    \
> +       instrument_copy_from_user_after((void *)&(x), ptr, sizeof(*(ptr)), 0); \
>         __builtin_expect(__ret_gu, 0);                                  \
>  })
>
> @@ -248,7 +251,9 @@ extern void __put_user_nocheck_8(void);
>
>  #define __put_user_size(x, ptr, size, label)                           \
>  do {                                                                   \
> +       __typeof__(*(ptr)) __pus_val = x;                               \
>         __chk_user_ptr(ptr);                                            \
> +       instrument_copy_to_user(ptr, &(__pus_val), size);               \
>         switch (size) {                                                 \
>         case 1:                                                         \
>                 __put_user_goto(x, ptr, "b", "iq", label);              \
> @@ -286,6 +291,7 @@ do {                                                                        \
>  #define __get_user_size(x, ptr, size, label)                           \
>  do {                                                                   \
>         __chk_user_ptr(ptr);                                            \
> +       instrument_copy_from_user_before((void *)&(x), ptr, size);      \
>         switch (size) {                                                 \
>         case 1: {                                                       \
>                 unsigned char x_u8__;                                   \
> @@ -305,6 +311,7 @@ do {                                                                        \
>         default:                                                        \
>                 (x) = __get_user_bad();                                 \
>         }                                                               \
> +       instrument_copy_from_user_after((void *)&(x), ptr, size, 0);    \
>  } while (0)
>
>  #define __get_user_asm(x, addr, itype, ltype, label)                   \
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>