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Fill RAM with random data using xorwow.

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xorwow provides significantly better random data, compared to previously
used function. Making it harder to predict what data RAM is filled with.
It adds a startup time of approx 80 ms, but can be compensated with
optimising other parts of the startup routine.

This changes both firmware and fpga hashes.

Signed-off-by: Joachim Strömbergson <joachim@assured.se>
This commit is contained in:
Joachim Strömbergson 2024-04-04 15:27:31 +02:00 • committed by dehanj
parent 09df7ae97f
commit eade3e11c5
No known key found for this signature in database
GPG key ID: 3707A9DBF4BB8F1A
3 changed files with 21 additions and 9 deletions
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26
hw/application_fpga/fw/tk1/main.c
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@ -54,6 +54,7 @@ static enum state loading_commands(const struct frame_header *hdr,
const uint8_t *cmd, enum state state,
struct context *ctx);
static void run(const struct context *ctx);
static uint32_t xorwow(uint32_t state, uint32_t acc);
static void scramble_ram(void);
static void print_hw_version(void)
@ -363,24 +364,35 @@ static void run(const struct context *ctx)
__builtin_unreachable();
}
static uint32_t xorwow(uint32_t state, uint32_t acc)
{
state ^= state << 13;
state ^= state >> 17;
state ^= state << 5;
state += acc;
return state;
}
static void scramble_ram(void)
{
uint32_t *ram = (uint32_t *)(TK1_RAM_BASE);
uint32_t rnd = rnd_word();
uint32_t rnd_incr = rnd_word();
// Set RAM address and data scrambling values
*ram_rand = rnd_word();
*ram_scramble = rnd_word();
// Fill RAM with random data (FW does not use RAM, has its stack in
// FW_RAM)
// Fill RAM with random data
// Get random state and accumulator seeds.
uint32_t data_state = rnd_word();
uint32_t data_acc = rnd_word();
for (uint32_t w = 0; w < TK1_RAM_SIZE / 4; w++) {
ram[w] = rnd;
rnd += rnd_incr;
data_state = xorwow(data_state, data_acc);
ram[w] = data_state;
}
// Set new scrambling values, for all use of RAM by app
// Set new address and RAM scrambling values,
// for all use of RAM by app.
*ram_rand = rnd_word();
*ram_scramble = rnd_word();
}