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    SubjectRe: [PATCH v4 04/45] x86: asm: instrument usercopy in get_user() and __put_user_size()
    On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@google.com> 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@google.com>
    > ---
    > 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
    >

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