Those are funny cases. Make sure they work. (Something is screwy with signal handling if a selector is 1, 2, or 3. Anyone who wants to dive into that rabbit hole is welcome to do so.) Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx> --- tools/testing/selftests/x86/fsgsbase.c | 41 +++++++++++++++++++++++++++++----- 1 file changed, 35 insertions(+), 6 deletions(-) diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c index b4967d875236..f249e042b3b5 100644 --- a/tools/testing/selftests/x86/fsgsbase.c +++ b/tools/testing/selftests/x86/fsgsbase.c @@ -285,9 +285,12 @@ static void *threadproc(void *ctx) } } -static void set_gs_and_switch_to(unsigned long local, unsigned long remote) +static void set_gs_and_switch_to(unsigned long local, + unsigned short force_sel, + unsigned long remote) { unsigned long base; + unsigned short sel_pre_sched, sel_post_sched; bool hard_zero = false; if (local == HARD_ZERO) { @@ -297,6 +300,8 @@ static void set_gs_and_switch_to(unsigned long local, unsigned long remote) printf("[RUN]\tARCH_SET_GS(0x%lx)%s, then schedule to 0x%lx\n", local, hard_zero ? " and clear gs" : "", remote); + if (force_sel) + printf("\tBefore schedule, set selector to 0x%hx\n", force_sel); if (syscall(SYS_arch_prctl, ARCH_SET_GS, local) != 0) err(1, "ARCH_SET_GS"); if (hard_zero) @@ -307,18 +312,35 @@ static void set_gs_and_switch_to(unsigned long local, unsigned long remote) printf("[FAIL]\tGSBASE wasn't set as expected\n"); } + if (force_sel) { + asm volatile ("mov %0, %%gs" : : "rm" (force_sel)); + sel_pre_sched = force_sel; + local = read_base(GS); + + /* + * Signal delivery seems to mess up weird selectors. Put it + * back. + */ + asm volatile ("mov %0, %%gs" : : "rm" (force_sel)); + } else { + asm volatile ("mov %%gs, %0" : "=rm" (sel_pre_sched)); + } + remote_base = remote; ftx = 1; syscall(SYS_futex, &ftx, FUTEX_WAKE, 0, NULL, NULL, 0); while (ftx != 0) syscall(SYS_futex, &ftx, FUTEX_WAIT, 1, NULL, NULL, 0); + asm volatile ("mov %%gs, %0" : "=rm" (sel_post_sched)); base = read_base(GS); - if (base == local) { - printf("[OK]\tGSBASE remained 0x%lx\n", local); + if (base == local && sel_pre_sched == sel_post_sched) { + printf("[OK]\tGS/BASE remained 0x%hx/0x%lx\n", + sel_pre_sched, local); } else { nerrs++; - printf("[FAIL]\tGSBASE changed to 0x%lx\n", base); + printf("[FAIL]\tGS/BASE changed from 0x%hx/0x%lx to 0x%hx/0x%lx\n", + sel_pre_sched, local, sel_post_sched, base); } } @@ -381,8 +403,15 @@ int main() for (int local = 0; local < 4; local++) { for (int remote = 0; remote < 4; remote++) { - set_gs_and_switch_to(bases_with_hard_zero[local], - bases_with_hard_zero[remote]); + for (unsigned short s = 0; s < 5; s++) { + unsigned short sel = s; + if (s == 4) + asm ("mov %%ss, %0" : "=rm" (sel)); + set_gs_and_switch_to( + bases_with_hard_zero[local], + sel, + bases_with_hard_zero[remote]); + } } } -- 2.13.3