[tor-bugs] #7419 [Tor]: Choose a faster memwipe implementation

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#7419: Choose a faster memwipe implementation
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 Reporter:  nickm        |          Owner:                  
     Type:  enhancement  |         Status:  new             
 Priority:  normal       |      Milestone:  Tor: unspecified
Component:  Tor          |        Version:                  
 Keywords:  tor-relay    |         Parent:                  
   Points:               |   Actualpoints:                  
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 Our current memwipe implementation (see #7352) was chosen for being very-
 likely-to-be-safe, not for its speed.  We could get much faster, probably:
 All we really need is a memwipe, plus some way to tell the compiler that
 the memwipe shouldn't be eliminated.

 One GCC-only option is
 {{{
 void memwipe(void *p, uint8_t b, size_t sz) __attribtue__((noinline));
 void memwipe(void *p, uint8_t b, size_t sz)
 {
    memset(p, b, sz);
 }
 }}}

 Another, crazier GCC-only option is
 {{{
 inline void
 memwipe(void *p, uint8_t b, size_t sz)
 {
    memset(p, b, sz);
    asm("" ::: "memory");
 }
 }}}

 And on windows, one could probably say
 {{{
 void
 memwipe(void *p, uint8_t b, size_t sz)
 {
    SecureZeroMemory(p, sz);
 }
 }}}
 if b == 0.

 Probably, we shouldn't bother to do any of these unless it turns out that
 OPENSSL_cleanse() is showing up in our profiles.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/7419>
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