On Tue, Jun 11, 2019 at 07:18:04PM +0200, Andrey Konovalov wrote:

On Tue, Jun 11, 2019 at 5:01 PM Catalin Marinas [off-list ref] wrote:

quoted

static void *tag_ptr(void *ptr)
{
        static int tagged_addr_err = 1;
        unsigned long tag = 0;

        if (tagged_addr_err == 1)
                tagged_addr_err = prctl(PR_SET_TAGGED_ADDR_CTRL,
                                        PR_TAGGED_ADDR_ENABLE, 0, 0, 0);

I think this requires atomics. malloc() can be called from multiple threads.

It's slightly racy but I assume in a real libc it can be initialised
earlier than the hook calls while still in single-threaded mode (I had
a quick attempt with __attribute__((constructor)) but didn't get far).

Even with the race, under normal circumstances calling the prctl() twice
is not a problem. I think the risk here is that someone disables the ABI
via sysctl and the ABI is enabled for some of the threads only.

-- 
Catalin

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