[PATCH] uml: check for differences in host support

If running on a host not supporting TLS (for instance 2.4) we should report that cleanly to the user, instead of printing not comprehensible "error 5" for that. Additionally, i386 and x86_64 support different ranges for user_desc->entry_number, and we must account for that; we couldn't pass ourselves -1 because we need to override previously existing TLS descriptors which glibc has possibly set, so test at startup the range to use. x86 and x86_64 existing ranges are hardcoded. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Acked-by: Jeff Dike <jdike@addtoit.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>

[PATCH] uml: check for differences in host support
If running on a host not supporting TLS (for instance 2.4) we should report that cleanly to the user, instead of printing not comprehensible "error 5" for that. Additionally, i386 and x86_64 support different ranges for user_desc->entry_number, and we must account for that; we couldn't pass ourselves -1 because we need to override previously existing TLS descriptors which glibc has possibly set, so test at startup the range to use. x86 and x86_64 existing ranges are hardcoded. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Acked-by: Jeff Dike <jdike@addtoit.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Paolo 'Blaisorblade' Giarrusso · Linus Torvalds
1 parent 54d8d3b5a0
Showing 8 changed files with 102 additions and 6 deletions Side-by-side Diff
arch/um/include/os.h
arch/um/include/sysdep-i386/tls.h
arch/um/include/user_util.h
arch/um/os-Linux/sys-i386/Makefile
arch/um/os-Linux/sys-i386/tls.c
arch/um/os-Linux/tls.c
arch/um/sys-i386/tls.c
include/asm-um/segment.h
@@ -173,6 +173,7 @@
 extern void os_early_checks(void);
 extern int can_do_skas(void);
 extern void os_check_bugs(void);
+extern void check_host_supports_tls(int *supports_tls, int *tls_min);
  
 /* Make sure they are clear when running in TT mode. Required by
  * SEGV_MAYBE_FIXABLE */
@@ -25,5 +25,9 @@
 typedef struct user_desc user_desc_t;
  
 # endif /* __KERNEL__ */
+
+#define GDT_ENTRY_TLS_MIN_I386 6
+#define GDT_ENTRY_TLS_MIN_X86_64 12
+
 #endif /* _SYSDEP_TLS_H */
@@ -8,6 +8,9 @@
  
 #include "sysdep/ptrace.h"
  
+/* Copied from kernel.h */
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
 #define CATCH_EINTR(expr) while ((errno = 0, ((expr) < 0)) && (errno == EINTR))
  
 extern int mode_tt;
@@ -3,7 +3,7 @@
 # Licensed under the GPL
 #
  
-obj-$(CONFIG_MODE_SKAS) = registers.o
+obj-$(CONFIG_MODE_SKAS) = registers.o tls.o
  
 USER_OBJS := $(obj-y)
  
+#include <linux/unistd.h>
+#include "sysdep/tls.h"
+#include "user_util.h"
+
+static _syscall1(int, get_thread_area, user_desc_t *, u_info);
+
+/* Checks whether host supports TLS, and sets *tls_min according to the value
+ * valid on the host.
+ * i386 host have it == 6; x86_64 host have it == 12, for i386 emulation. */
+void check_host_supports_tls(int *supports_tls, int *tls_min) {
+	/* Values for x86 and x86_64.*/
+	int val[] = {GDT_ENTRY_TLS_MIN_I386, GDT_ENTRY_TLS_MIN_X86_64};
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(val); i++) {
+		user_desc_t info;
+		info.entry_number = val[i];
+
+		if (get_thread_area(&info) == 0) {
+			*tls_min = val[i];
+			*supports_tls = 1;
+			return;
+		} else {
+			if (errno == EINVAL)
+				continue;
+			else if (errno == ENOSYS)
+				*supports_tls = 0;
+				return;
+		}
+	}
+
+	*supports_tls = 0;
+}
@@ -48,8 +48,8 @@
 #ifdef UML_CONFIG_MODE_TT
 #include "linux/unistd.h"
  
-_syscall1(int, get_thread_area, user_desc_t *, u_info);
-_syscall1(int, set_thread_area, user_desc_t *, u_info);
+static _syscall1(int, get_thread_area, user_desc_t *, u_info);
+static _syscall1(int, set_thread_area, user_desc_t *, u_info);
  
 int do_set_thread_area_tt(user_desc_t *info)
 {
@@ -24,6 +24,10 @@
 #include "skas.h"
 #endif
  
+/* If needed we can detect when it's uninitialized. */
+static int host_supports_tls = -1;
+int host_gdt_entry_tls_min = -1;
+
 #ifdef CONFIG_MODE_SKAS
 int do_set_thread_area_skas(struct user_desc *info)
 {
  
  
@@ -157,11 +161,20 @@
 	}
 }
  
-/* This in SKAS0 does not need to be used, since we have different host
- * processes. Nor will this need to be used when we'll add support to the host
+/* In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
+ * common host process. So this is needed in SKAS0 too.
+ *
+ * However, if each thread had a different host process (and this was discussed
+ * for SMP support) this won't be needed.
+ *
+ * And this will not need be used when (and if) we'll add support to the host
  * SKAS patch. */
+
 int arch_switch_tls_skas(struct task_struct *from, struct task_struct *to)
 {
+	if (!host_supports_tls)
+		return 0;
+
 	/* We have no need whatsoever to switch TLS for kernel threads; beyond
 	 * that, that would also result in us calling os_set_thread_area with
 	 * userspace_pid[cpu] == 0, which gives an error. */
@@ -173,6 +186,9 @@
  
 int arch_switch_tls_tt(struct task_struct *from, struct task_struct *to)
 {
+	if (!host_supports_tls)
+		return 0;
+
 	if (needs_TLS_update(to))
 		return load_TLS(0, to);
  
@@ -256,6 +272,9 @@
 	struct user_desc info;
 	int idx, ret;
  
+	if (!host_supports_tls)
+		return -ENOSYS;
+
 	if (copy_from_user(&info, user_desc, sizeof(info)))
 		return -EFAULT;
  
@@ -287,6 +306,9 @@
 {
 	struct user_desc info;
  
+	if (!host_supports_tls)
+		return -EIO;
+
 	if (copy_from_user(&info, user_desc, sizeof(info)))
 		return -EFAULT;
  
@@ -298,6 +320,9 @@
 	struct user_desc info;
 	int idx, ret;
  
+	if (!host_supports_tls)
+		return -ENOSYS;
+
 	if (get_user(idx, &user_desc->entry_number))
 		return -EFAULT;
  
@@ -321,6 +346,9 @@
 	struct user_desc info;
 	int ret;
  
+	if (!host_supports_tls)
+		return -EIO;
+
 	ret = get_tls_entry(child, &info, idx);
 	if (ret < 0)
 		goto out;
@@ -330,4 +358,28 @@
 out:
 	return ret;
 }
+
+
+/* XXX: This part is probably common to i386 and x86-64. Don't create a common
+ * file for now, do that when implementing x86-64 support.*/
+static int __init __setup_host_supports_tls(void) {
+	check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
+	if (host_supports_tls) {
+		printk(KERN_INFO "Host TLS support detected\n");
+		printk(KERN_INFO "Detected host type: ");
+		switch (host_gdt_entry_tls_min) {
+			case GDT_ENTRY_TLS_MIN_I386:
+				printk("i386\n");
+				break;
+			case GDT_ENTRY_TLS_MIN_X86_64:
+				printk("x86_64\n");
+				break;
+		}
+	} else
+		printk(KERN_ERR "  Host TLS support NOT detected! "
+				"TLS support inside UML will not work\n");
+	return 1;
+}
+
+__initcall(__setup_host_supports_tls);
 #ifndef __UM_SEGMENT_H
 #define __UM_SEGMENT_H
  
-#include "asm/arch/segment.h"
+extern int host_gdt_entry_tls_min;
+
+#define GDT_ENTRY_TLS_ENTRIES 3
+#define GDT_ENTRY_TLS_MIN host_gdt_entry_tls_min
+#define GDT_ENTRY_TLS_MAX (GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)
  
 #endif
...	...	@@ -173,6 +173,7 @@
173	173	extern void os_early_checks(void);
174	174	extern int can_do_skas(void);
175	175	extern void os_check_bugs(void);
	176	+extern void check_host_supports_tls(int supports_tls, int tls_min);
176	177
177	178	/* Make sure they are clear when running in TT mode. Required by
178	179	* SEGV_MAYBE_FIXABLE */
...	...	@@ -25,5 +25,9 @@
25	25	typedef struct user_desc user_desc_t;
26	26
27	27	# endif /* __KERNEL__ */
	28	+
	29	+#define GDT_ENTRY_TLS_MIN_I386 6
	30	+#define GDT_ENTRY_TLS_MIN_X86_64 12
	31	+
28	32	#endif /* _SYSDEP_TLS_H */
...	...	@@ -8,6 +8,9 @@
8	8
9	9	#include "sysdep/ptrace.h"
10	10
	11	+/* Copied from kernel.h */
	12	+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
	13	+
11	14	#define CATCH_EINTR(expr) while ((errno = 0, ((expr) < 0)) && (errno == EINTR))
12	15
13	16	extern int mode_tt;
...	...	@@ -3,7 +3,7 @@
3	3	# Licensed under the GPL
4	4	#
5	5
6		-obj-$(CONFIG_MODE_SKAS) = registers.o
	6	+obj-$(CONFIG_MODE_SKAS) = registers.o tls.o
7	7
8	8	USER_OBJS := $(obj-y)
9	9
	1	+#include <linux/unistd.h>
	2	+#include "sysdep/tls.h"
	3	+#include "user_util.h"
	4	+
	5	+static _syscall1(int, get_thread_area, user_desc_t *, u_info);
	6	+
	7	+/* Checks whether host supports TLS, and sets *tls_min according to the value
	8	+ * valid on the host.
	9	+ * i386 host have it == 6; x86_64 host have it == 12, for i386 emulation. */
	10	+void check_host_supports_tls(int supports_tls, int tls_min) {
	11	+ /* Values for x86 and x86_64.*/
	12	+ int val[] = {GDT_ENTRY_TLS_MIN_I386, GDT_ENTRY_TLS_MIN_X86_64};
	13	+ int i;
	14	+
	15	+ for (i = 0; i < ARRAY_SIZE(val); i++) {
	16	+ user_desc_t info;
	17	+ info.entry_number = val[i];
	18	+
	19	+ if (get_thread_area(&info) == 0) {
	20	+ *tls_min = val[i];
	21	+ *supports_tls = 1;
	22	+ return;
	23	+ } else {
	24	+ if (errno == EINVAL)
	25	+ continue;
	26	+ else if (errno == ENOSYS)
	27	+ *supports_tls = 0;
	28	+ return;
	29	+ }
	30	+ }
	31	+
	32	+ *supports_tls = 0;
	33	+}
...	...	@@ -48,8 +48,8 @@
48	48	#ifdef UML_CONFIG_MODE_TT
49	49	#include "linux/unistd.h"
50	50
51		-_syscall1(int, get_thread_area, user_desc_t *, u_info);
52		-_syscall1(int, set_thread_area, user_desc_t *, u_info);
	51	+static _syscall1(int, get_thread_area, user_desc_t *, u_info);
	52	+static _syscall1(int, set_thread_area, user_desc_t *, u_info);
53	53
54	54	int do_set_thread_area_tt(user_desc_t *info)
55	55	{
...	...	@@ -24,6 +24,10 @@
24	24	#include "skas.h"
25	25	#endif
26	26
	27	+/* If needed we can detect when it's uninitialized. */
	28	+static int host_supports_tls = -1;
	29	+int host_gdt_entry_tls_min = -1;
	30	+
27	31	#ifdef CONFIG_MODE_SKAS
28	32	int do_set_thread_area_skas(struct user_desc *info)
29	33	{
30	34
31	35
...	...	@@ -157,11 +161,20 @@
157	161	}
158	162	}
159	163
160		-/* This in SKAS0 does not need to be used, since we have different host
161		- * processes. Nor will this need to be used when we'll add support to the host
	164	+/* In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
	165	+ * common host process. So this is needed in SKAS0 too.
	166	+ *
	167	+ * However, if each thread had a different host process (and this was discussed
	168	+ * for SMP support) this won't be needed.
	169	+ *
	170	+ * And this will not need be used when (and if) we'll add support to the host
162	171	* SKAS patch. */
	172	+
163	173	int arch_switch_tls_skas(struct task_struct from, struct task_struct to)
164	174	{
	175	+ if (!host_supports_tls)
	176	+ return 0;
	177	+
165	178	/* We have no need whatsoever to switch TLS for kernel threads; beyond
166	179	* that, that would also result in us calling os_set_thread_area with
167	180	* userspace_pid[cpu] == 0, which gives an error. */
...	...	@@ -173,6 +186,9 @@
173	186
174	187	int arch_switch_tls_tt(struct task_struct from, struct task_struct to)
175	188	{
	189	+ if (!host_supports_tls)
	190	+ return 0;
	191	+
176	192	if (needs_TLS_update(to))
177	193	return load_TLS(0, to);
178	194
...	...	@@ -256,6 +272,9 @@
256	272	struct user_desc info;
257	273	int idx, ret;
258	274
	275	+ if (!host_supports_tls)
	276	+ return -ENOSYS;
	277	+
259	278	if (copy_from_user(&info, user_desc, sizeof(info)))
260	279	return -EFAULT;
261	280
...	...	@@ -287,6 +306,9 @@
287	306	{
288	307	struct user_desc info;
289	308
	309	+ if (!host_supports_tls)
	310	+ return -EIO;
	311	+
290	312	if (copy_from_user(&info, user_desc, sizeof(info)))
291	313	return -EFAULT;
292	314
...	...	@@ -298,6 +320,9 @@
298	320	struct user_desc info;
299	321	int idx, ret;
300	322
	323	+ if (!host_supports_tls)
	324	+ return -ENOSYS;
	325	+
301	326	if (get_user(idx, &user_desc->entry_number))
302	327	return -EFAULT;
303	328
...	...	@@ -321,6 +346,9 @@
321	346	struct user_desc info;
322	347	int ret;
323	348
	349	+ if (!host_supports_tls)
	350	+ return -EIO;
	351	+
324	352	ret = get_tls_entry(child, &info, idx);
325	353	if (ret < 0)
326	354	goto out;
...	...	@@ -330,4 +358,28 @@
330	358	out:
331	359	return ret;
332	360	}
	361	+
	362	+
	363	+/* XXX: This part is probably common to i386 and x86-64. Don't create a common
	364	+ * file for now, do that when implementing x86-64 support.*/
	365	+static int __init __setup_host_supports_tls(void) {
	366	+ check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
	367	+ if (host_supports_tls) {
	368	+ printk(KERN_INFO "Host TLS support detected\n");
	369	+ printk(KERN_INFO "Detected host type: ");
	370	+ switch (host_gdt_entry_tls_min) {
	371	+ case GDT_ENTRY_TLS_MIN_I386:
	372	+ printk("i386\n");
	373	+ break;
	374	+ case GDT_ENTRY_TLS_MIN_X86_64:
	375	+ printk("x86_64\n");
	376	+ break;
	377	+ }
	378	+ } else
	379	+ printk(KERN_ERR " Host TLS support NOT detected! "
	380	+ "TLS support inside UML will not work\n");
	381	+ return 1;
	382	+}
	383	+
	384	+__initcall(__setup_host_supports_tls);
1	1	#ifndef __UM_SEGMENT_H
2	2	#define __UM_SEGMENT_H
3	3
4		-#include "asm/arch/segment.h"
	4	+extern int host_gdt_entry_tls_min;
	5	+
	6	+#define GDT_ENTRY_TLS_ENTRIES 3
	7	+#define GDT_ENTRY_TLS_MIN host_gdt_entry_tls_min
	8	+#define GDT_ENTRY_TLS_MAX (GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)
5	9
6	10	#endif