On Fri, Sep 06, 2019 at 10:49:19AM +0300, Evgeny Yakovlev wrote:
> Commit 18a34cce introduced init_apic_map. It iterates over
> sizeof(online_cpus) * 8 items and sets APIC ids in id_map.
> However, online_cpus is defined (in x86/cstart[64].S) as a 64-bit
> variable. After i >= 64, init_apic_map begins to read out of bounds of
> online_cpus. If it finds a non-zero value there enough times,
> it then proceeds to potentially overflow id_map in assignment.
>
> In our test case id_map was linked close to pg_base. As a result page
> table was corrupted and we've seen sporadic failures of ioapic test.
>
> Signed-off-by: Evgeny Yakovlev <wrfsh@xxxxxxxxxxxxxx>
> ---
> lib/x86/apic.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/lib/x86/apic.c b/lib/x86/apic.c
> index 504299e..1ed8bab 100644
> --- a/lib/x86/apic.c
> +++ b/lib/x86/apic.c
> @@ -228,14 +228,17 @@ void mask_pic_interrupts(void)
> outb(0xff, 0xa1);
> }
>
> -extern unsigned char online_cpus[256 / 8];
The immediate issue can be resolved simply by fixing this definition.
> +/* Should hold MAX_TEST_CPUS bits */
> +extern uint64_t online_cpus;
>
> void init_apic_map(void)
> {
> unsigned int i, j = 0;
>
> - for (i = 0; i < sizeof(online_cpus) * 8; i++) {
> - if ((1ul << (i % 8)) & (online_cpus[i / 8]))
> + assert(MAX_TEST_CPUS <= sizeof(online_cpus) * 8);
> +
> + for (i = 0; i < MAX_TEST_CPUS; i++) {
> + if (online_cpus & ((uint64_t)1 << i))
This is functionally correct, but it's just as easy to have online_cpus
sized based on MAX_TEST_CPUS, i.e. to allow MAX_TEST_CPUS to be changed
at will (within reason). I'll send patches.
> id_map[j++] = i;
> }
> }
> --
> 2.7.4
>
