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Message-Id: <20181023184234.14025-10-chang.seok.bae@intel.com>
Date: Tue, 23 Oct 2018 11:42:31 -0700
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Andy Lutomirski <luto@...nel.org>,
"H . Peter Anvin" <hpa@...or.com>
Cc: Andi Kleen <ak@...ux.intel.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Markus T Metzger <markus.t.metzger@...el.com>,
Ravi Shankar <ravi.v.shankar@...el.com>,
"Chang S . Bae" <chang.seok.bae@...el.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: [v3 09/12] selftests/x86/fsgsbase: Test WRGSBASE
From: Andy Lutomirski <luto@...nel.org>
This validates that GS and GSBASE are independently preserved across
context switches.
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Reviewed-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
---
tools/testing/selftests/x86/fsgsbase.c | 110 ++++++++++++++++++++++++-
1 file changed, 107 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index f249e042b3b5..fe7acfef53ba 100644
--- a/tools/testing/selftests/x86/fsgsbase.c
+++ b/tools/testing/selftests/x86/fsgsbase.c
@@ -23,6 +23,7 @@
#include <pthread.h>
#include <asm/ldt.h>
#include <sys/mman.h>
+#include <setjmp.h>
#ifndef __x86_64__
# error This test is 64-bit only
@@ -71,6 +72,51 @@ static void sigsegv(int sig, siginfo_t *si, void *ctx_void)
}
+static jmp_buf jmpbuf;
+
+static void sigill(int sig, siginfo_t *si, void *ctx_void)
+{
+ siglongjmp(jmpbuf, 1);
+}
+
+static bool have_fsgsbase;
+
+static inline unsigned long rdgsbase(void)
+{
+ unsigned long gsbase;
+
+ asm volatile(".byte 0xf3,0x48,0x0f,0xae,0xc8 # rdgsbaseq %%rax"
+ : "=a" (gsbase)
+ :: "memory");
+
+ return gsbase;
+}
+
+static inline unsigned long rdfsbase(void)
+{
+ unsigned long fsbase;
+
+ asm volatile(".byte 0xf3,0x48,0x0f,0xae,0xc0 # rdfsbaseq %%rax"
+ : "=a" (fsbase)
+ :: "memory");
+
+ return fsbase;
+}
+
+static inline void wrgsbase(unsigned long gsbase)
+{
+ asm volatile(".byte 0xf3,0x48,0x0f,0xae,0xd8 # wrgsbaseq %%rax"
+ :: "a" (gsbase)
+ : "memory");
+}
+
+static inline void wrfsbase(unsigned long fsbase)
+{
+ asm volatile(".byte 0xf3,0x48,0x0f,0xae,0xd0 # wrfsbaseq %%rax"
+ :: "a" (fsbase)
+ : "memory");
+}
+
enum which_base { FS, GS };
static unsigned long read_base(enum which_base which)
@@ -199,14 +245,16 @@ static void do_remote_base()
to_set, hard_zero ? " and clear gs" : "", sel);
}
-void do_unexpected_base(void)
+static __thread int set_thread_area_entry_number = -1;
+
+static void do_unexpected_base(void)
{
/*
* The goal here is to try to arrange for GS == 0, GSBASE !=
* 0, and for the the kernel the think that GSBASE == 0.
*
* To make the test as reliable as possible, this uses
- * explicit descriptorss. (This is not the only way. This
+ * explicit descriptors. (This is not the only way. This
* could use ARCH_SET_GS with a low, nonzero base, but the
* relevant side effect of ARCH_SET_GS could change.)
*/
@@ -239,7 +287,7 @@ void do_unexpected_base(void)
MAP_PRIVATE | MAP_ANONYMOUS | MAP_32BIT, -1, 0);
memcpy(low_desc, &desc, sizeof(desc));
- low_desc->entry_number = -1;
+ low_desc->entry_number = set_thread_area_entry_number;
/* 32-bit set_thread_area */
long ret;
@@ -254,6 +302,8 @@ void do_unexpected_base(void)
return;
}
printf("\tother thread: using GDT slot %d\n", desc.entry_number);
+ set_thread_area_entry_number = desc.entry_number;
+
asm volatile ("mov %0, %%gs" : : "rm" ((unsigned short)((desc.entry_number << 3) | 0x3)));
}
@@ -265,6 +315,34 @@ void do_unexpected_base(void)
asm volatile ("mov %0, %%gs" : : "rm" ((unsigned short)0));
}
+void test_wrbase(unsigned short index, unsigned long base)
+{
+ unsigned short newindex;
+ unsigned long newbase;
+
+ printf("[RUN]\tGS = 0x%hx, GSBASE = 0x%lx\n", index, base);
+
+ asm volatile ("mov %0, %%gs" : : "rm" (index));
+ wrgsbase(base);
+
+ remote_base = 0;
+ 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" (newindex));
+ newbase = rdgsbase();
+
+ if (newindex == index && newbase == base) {
+ printf("[OK]\tIndex and base were preserved\n");
+ } else {
+ printf("[FAIL]\tAfter switch, GS = 0x%hx and GSBASE = 0x%lx\n",
+ newindex, newbase);
+ nerrs++;
+ }
+}
+
static void *threadproc(void *ctx)
{
while (1) {
@@ -371,6 +449,17 @@ int main()
{
pthread_t thread;
+ /* Probe FSGSBASE */
+ sethandler(SIGILL, sigill, 0);
+ if (sigsetjmp(jmpbuf, 1) == 0) {
+ rdfsbase();
+ have_fsgsbase = true;
+ printf("\tFSGSBASE instructions are enabled\n");
+ } else {
+ printf("\tFSGSBASE instructions are disabled\n");
+ }
+ clearhandler(SIGILL);
+
sethandler(SIGSEGV, sigsegv, 0);
check_gs_value(0);
@@ -417,6 +506,21 @@ int main()
test_unexpected_base();
+ if (have_fsgsbase) {
+ unsigned short ss;
+
+ asm volatile ("mov %%ss, %0" : "=rm" (ss));
+
+ test_wrbase(0, 0);
+ test_wrbase(0, 1);
+ test_wrbase(0, 0x200000000);
+ test_wrbase(0, 0xffffffffffffffff);
+ test_wrbase(ss, 0);
+ test_wrbase(ss, 1);
+ test_wrbase(ss, 0x200000000);
+ test_wrbase(ss, 0xffffffffffffffff);
+ }
+
ftx = 3; /* Kill the thread. */
syscall(SYS_futex, &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
--
2.19.1
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