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Subject[PATCH 4.9 06/14] selftests/x86/fsgsbase: Test selectors 1, 2, and 3
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Lutomirski <luto@kernel.org>

commit 23d98c204386a98d9ef9f9e744f41443ece4929f upstream.

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.)

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang Seok <chang.seok.bae@intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
tools/testing/selftests/x86/fsgsbase.c | 41 ++++++++++++++++++++++++++++-----
1 file changed, 35 insertions(+), 6 deletions(-)

--- 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(unsigne

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(unsigne
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]);
+ }
}
}


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