Il 19/08/2014 15:04, Nadav Amit ha scritto:
> Commit 5045b46803 added a check that cs.dpl equals cs.rpl during task-switch.
> This is a wrong check, and this patch introduces a test in which cs.dpl !=
> cs.rpl. To do so, it configures tss.cs to be conforming with rpl=3 and dpl=0.
> Since the cpl after calling is 3, it does not make any prints in the callee.
>
> Signed-off-by: Nadav Amit <[email protected]>
> ---
> x86/taskswitch2.c | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/x86/taskswitch2.c b/x86/taskswitch2.c
> index 92fc941..1fe833e 100644
> --- a/x86/taskswitch2.c
> +++ b/x86/taskswitch2.c
> @@ -7,6 +7,7 @@
>
> #define MAIN_TSS_SEL (FIRST_SPARE_SEL + 0)
> #define VM86_TSS_SEL (FIRST_SPARE_SEL + 8)
> +#define CONFORM_CS_SEL (FIRST_SPARE_SEL + 16)
>
> static volatile int test_count;
> static volatile unsigned int test_divider;
> @@ -102,6 +103,14 @@ start:
> goto start;
> }
>
> +static void user_tss(void)
> +{
> +start:
> + test_count++;
> + asm volatile ("iret");
> + goto start;
> +}
> +
> void test_kernel_mode_int()
> {
> unsigned int res;
> @@ -248,6 +257,19 @@ void test_vm86_switch(void)
> report("VM86", 1);
> }
>
> +void test_conforming_switch(void)
> +{
> + /* test lcall with conforming segment, cs.dpl != cs.rpl */
> + test_count = 0;
> + set_intr_task_gate(0, user_tss);
No need to use set_intr_task_gate, since the IDT is not involved here.
tss_intr.eip = (u32)user_tss;
is enough.
I fixed this up and applied the patch. Thanks!
Paolo
> +
> + tss_intr.cs = CONFORM_CS_SEL | 3;
> + tss_intr.ds = tss_intr.gs = tss_intr.fs = tss_intr.ss = USER_DS;
> + set_gdt_entry(CONFORM_CS_SEL, 0, 0xffffffff, 0x9f, 0xc0);
> + asm volatile("lcall $" xstr(TSS_INTR) ", $0xf4f4f4f4");
> + report("lcall with cs.rpl != cs.dpl", test_count == 1);
> +}
> +
> int main()
> {
> setup_vm();
> @@ -256,6 +278,7 @@ int main()
>
> test_kernel_mode_int();
> test_vm86_switch();
> + test_conforming_switch();
>
> return report_summary();
> }
>
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