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From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>, Andy Lutomirski <luto@kernel.org>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Andi Kleen <ak@linux.intel.com>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>,
	"Chang S . Bae" <chang.seok.bae@intel.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: [RESEND PATCH v6 09/12] selftests/x86/fsgsbase: Test WRGSBASE
Date: Fri, 15 Mar 2019 13:06:42 -0700
Message-ID: <1552680405-5265-10-git-send-email-chang.seok.bae@intel.com> (raw)
In-Reply-To: <1552680405-5265-1-git-send-email-chang.seok.bae@intel.com>

From: Andy Lutomirski <luto@kernel.org>

This validates that GS and GSBASE are independently preserved across
context switches.

[ chang: Use FSGSBASE instructions directly instead of .byte ]

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
---
 tools/testing/selftests/x86/fsgsbase.c | 102 ++++++++++++++++++++++++-
 1 file changed, 99 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index f249e042b3b5..5956475972f1 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 +72,43 @@ 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("rdgsbase %0" : "=r" (gsbase) :: "memory");
+
+	return gsbase;
+}
+
+static inline unsigned long rdfsbase(void)
+{
+	unsigned long fsbase;
+
+	asm volatile("rdfsbase %0" : "=r" (fsbase) :: "memory");
+
+	return fsbase;
+}
+
+static inline void wrgsbase(unsigned long gsbase)
+{
+	asm volatile("wrgsbase %0" :: "r" (gsbase) : "memory");
+}
+
+static inline void wrfsbase(unsigned long fsbase)
+{
+	asm volatile("wrfsbase %0" :: "r" (fsbase) : "memory");
+}
+
 enum which_base { FS, GS };
 
 static unsigned long read_base(enum which_base which)
@@ -199,14 +237,16 @@ 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 +279,7 @@ 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 +294,8 @@ 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 +307,34 @@ 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 +441,17 @@ 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 +498,21 @@ 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


  parent reply index

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-15 20:06 [RESEND PATCH v6 00/12] x86: Enable FSGSBASE instructions Chang S. Bae
2019-03-15 20:06 ` [RESEND PATCH v6 01/12] x86/fsgsbase/64: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Chang S. Bae
2019-03-15 20:06 ` [RESEND PATCH v6 02/12] kbuild: Raise the minimum required binutils version to 2.21 Chang S. Bae
2019-03-15 20:06 ` [RESEND PATCH v6 03/12] x86/fsgsbase/64: Add intrinsics for FSGSBASE instructions Chang S. Bae
2019-03-15 20:06 ` [RESEND PATCH v6 04/12] x86/fsgsbase/64: Enable FSGSBASE instructions in the helper functions Chang S. Bae
2019-03-25 11:38   ` Thomas Gleixner
2019-03-25 12:46     ` Thomas Gleixner
2019-03-25 13:05       ` Thomas Gleixner
2019-03-26  0:38     ` Andi Kleen
2019-03-26 15:01       ` New feature/ABI review process [was Re: [RESEND PATCH v6 04/12] x86/fsgsbase/64:..] Thomas Gleixner
2019-03-26 22:56         ` Andi Kleen
2019-03-27 21:15           ` Thomas Gleixner
2019-03-15 20:06 ` [RESEND PATCH v6 05/12] x86/fsgsbase/64: Preserve FS/GS state in __switch_to() if FSGSBASE is on Chang S. Bae
2019-03-15 20:06 ` [RESEND PATCH v6 06/12] x86/fsgsbase/64: When copying a thread, use the FSGSBASE instructions if available Chang S. Bae
2019-03-15 20:06 ` [RESEND PATCH v6 07/12] x86/fsgsbase/64: Introduce the FIND_PERCPU_BASE macro Chang S. Bae
2019-03-25  9:02   ` Thomas Gleixner
2019-05-01 13:52     ` Bae, Chang Seok
2019-03-15 20:06 ` [RESEND PATCH v6 08/12] x86/fsgsbase/64: Use the per-CPU base as GSBASE at the paranoid_entry Chang S. Bae
2019-03-25  9:44   ` Thomas Gleixner
2019-04-05  8:35     ` Thomas Gleixner
2019-04-05 13:50       ` Andy Lutomirski
2019-05-01 13:52         ` Bae, Chang Seok
2019-05-01 17:40           ` Andy Lutomirski
2019-05-01 18:01             ` Bae, Chang Seok
     [not found]               ` <7029A32B-958E-4C1E-8B5F-D49BA68E4755@intel.com>
2019-05-01 20:25                 ` Andy Lutomirski
2019-05-01 21:04                   ` Bae, Chang Seok
2019-05-02  0:29                     ` Andy Lutomirski
2019-05-06 22:56     ` Bae, Chang Seok
2019-03-15 20:06 ` Chang S. Bae [this message]
2019-03-15 20:06 ` [RESEND PATCH v6 10/12] x86/fsgsbase/64: Enable FSGSBASE by default and add a chicken bit Chang S. Bae
2019-03-15 20:06 ` [RESEND PATCH v6 11/12] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Chang S. Bae
2019-03-15 20:06 ` [RESEND PATCH v6 12/12] x86/fsgsbase/64: Add documentation for FSGSBASE Chang S. Bae
2019-03-30 16:15   ` Randy Dunlap
2019-03-26  0:43 ` [RESEND PATCH v6 00/12] x86: Enable FSGSBASE instructions Andy Lutomirski

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