Re: [PATCH v4] x86: add failure injection to get/put/clear_user

[Alexander Potapenko]

(Albert's @google.com address is gone, removing it from CC list)

On Fri, Oct 23, 2020 at 10:16 AM Alexander Potapenko <glider@xxxxxxxxxx> wrote:
>
> From: Albert van der Linde <alinde@xxxxxxxxxx>
>
> To test fault-tolerance of user memory acceses in x86, add support for
> fault injection.
>
> Make both put_user() and get_user() fail with -EFAULT, and clear_user()
> fail by not clearing any bytes.
>
> Reviewed-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
> Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>
> Signed-off-by: Albert van der Linde <alinde@xxxxxxxxxx>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
>
> ---
> v2:
>  - no significant changes
>
> v3:
>  - no changes
>
> v4:
>  - instrument the new out-of-line implementations of get_user()/put_user()
>  - fix a minor checkpatch warning in the inline assembly
>
> ---
> ---
>  arch/x86/include/asm/uaccess.h | 36 ++++++++++++++++++++++------------
>  arch/x86/lib/usercopy_64.c     |  3 +++
>  2 files changed, 26 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index f13659523108..7041ebc48b75 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/fault-inject-usercopy.h>
>  #include <linux/kasan-checks.h>
>  #include <linux/string.h>
>  #include <asm/asm.h>
> @@ -126,11 +127,16 @@ extern int __get_user_bad(void);
>         int __ret_gu;                                                   \
>         register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX);            \
>         __chk_user_ptr(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;                    \
> +       if (should_fail_usercopy()) {                                   \
> +               (x) = 0;                                                \
> +               __ret_gu = -EFAULT;                                     \
> +       } else {                                                        \
> +               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;            \
> +       }                                                               \
>         __builtin_expect(__ret_gu, 0);                                  \
>  })
>
> @@ -213,14 +219,18 @@ extern void __put_user_nocheck_8(void);
>         int __ret_pu;                                                   \
>         register __typeof__(*(ptr)) __val_pu asm("%"_ASM_AX);           \
>         __chk_user_ptr(ptr);                                            \
> -       __val_pu = (x);                                                 \
> -       asm volatile("call __" #fn "_%P[size]"                          \
> -                    : "=c" (__ret_pu),                                 \
> -                       ASM_CALL_CONSTRAINT                             \
> -                    : "0" (ptr),                                       \
> -                      "r" (__val_pu),                                  \
> -                      [size] "i" (sizeof(*(ptr)))                      \
> -                    :"ebx");                                           \
> +       if (unlikely(should_fail_usercopy())) {                         \
> +               __ret_pu = -EFAULT;                                     \
> +       } else {                                                        \
> +               __val_pu = (x);                                         \
> +               asm volatile("call __" #fn "_%P[size]"                  \
> +                            : "=c" (__ret_pu),                         \
> +                               ASM_CALL_CONSTRAINT                     \
> +                            : "0" (ptr),                               \
> +                              "r" (__val_pu),                          \
> +                              [size] "i" (sizeof(*(ptr)))              \
> +                            : "ebx");                                  \
> +       }                                                               \
>         __builtin_expect(__ret_pu, 0);                                  \
>  })
>
> diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
> index 508c81e97ab1..5617b3864586 100644
> --- a/arch/x86/lib/usercopy_64.c
> +++ b/arch/x86/lib/usercopy_64.c
> @@ -7,6 +7,7 @@
>   * Copyright 2002 Andi Kleen <ak@xxxxxxx>
>   */
>  #include <linux/export.h>
> +#include <linux/fault-inject-usercopy.h>
>  #include <linux/uaccess.h>
>  #include <linux/highmem.h>
>
> @@ -50,6 +51,8 @@ EXPORT_SYMBOL(__clear_user);
>
>  unsigned long clear_user(void __user *to, unsigned long n)
>  {
> +       if (should_fail_usercopy())
> +               return n;
>         if (access_ok(to, n))
>                 return __clear_user(to, n);
>         return n;
> --
> 2.29.0.rc2.309.g374f81d7ae-goog
>


-- 
Alexander Potapenko
Software Engineer

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