On 9/24/2020 6:07 AM, Borislav Petkov wrote:
On Wed, Sep 23, 2020 at 04:10:43PM -0700, Dave Jiang wrote:+/* The dst parameter must be 64-bytes aligned */ +static inline void movdir64b(void *dst, const void *src) +{ + /* + * Note that this isn't an "on-stack copy", just definition of "dst" + * as a pointer to 64-bytes of stuff that is going to be overwritten. + * In the MOVDIR64B case that may be needed as you can use the + * MOVDIR64B instruction to copy arbitrary memory around. This trick + * lets the compiler know how much gets clobbered. + */ + volatile struct { char _[64]; } *__dst = dst; + + /* MOVDIR64B [rdx], rax */ + asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02" + : + : "m" (*(struct { char _[64];} **)src), "a" (__dst) + : "memory"); +}Ok, Micha and I hashed it out on IRC, here's what you do. Please keep the comments too because we will forget soon again. static inline void movdir64b(void *__dst, const void *src) { struct { char _[64]; } *__src = src; struct { char _[64]; } *__dst = dst; /* * MOVDIR64B %(rdx), rax. * * Both __src and __dst must be memory constraints in order to tell the * compiler that no other memory accesses should be reordered around * this one. * * Also, both must be supplied as lvalues because this tells * the compiler what the object is (its size) the instruction accesses. * I.e., not the pointers but what they point, thus the deref'ing '*'. */ asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02" : "+m" (*__dst) : "m" (*__src), "a" (__dst), "d" (__src)); }
Thanks Boris. I will update and resend.
Thx.
