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performance(sqlcipher): Fix burn_stack performance issue 

Fixing status-im/status-desktop#10572

Implements a cross-platform version of OP-TEE/optee_os#3102

Remove recursion
Use memset instead of while loop
A description to understand introduced changes without reading the code.

zeromem weights about 50% of the total CPU time on M1 Macs and seems to be major performance offender.
It is used to clear the stack when using variables with sensitive information.
This commit is contained in:
Alex Jbanca 2023-05-09 16:21:44 +03:00
parent 55dbde1788
commit d4fa1002f9
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GPG Key ID: 6004079575C21C5D
2 changed files with 12 additions and 7 deletions
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4
burn_stack.c
View File

@ -21,10 +21,8 @@
*/
void burn_stack(unsigned long len)
{
unsigned char buf[32];
unsigned char buf[len];
zeromem(buf, sizeof(buf));
if (len > (unsigned long)sizeof(buf))
burn_stack(len - sizeof(buf));
}

15
zeromem.c
View File

@ -9,12 +9,22 @@
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
*/
#include "tomcrypt.h"
#include <string.h>
/**
@file zeromem.c
Zero a block of memory, Tom St Denis
*/
/*
* Pointer to memset is volatile so that compiler must de-reference
* the pointer and can't assume that it points to any function in
* particular (such as memset, which it then might further "optimize")
*/
typedef void *(*memset_t)(void *, int, size_t);
static volatile memset_t memset_func = memset;
/**
Zero a block of memory
@param out The destination of the area to zero
@ -22,11 +32,8 @@
*/
void zeromem(void *out, size_t outlen)
{
unsigned char *mem = out;
LTC_ARGCHKVD(out != NULL);
while (outlen-- > 0) {
*mem++ = 0;
}
memset_func((void *)out, 0, outlen);
}
/* $Source$ */