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device-drivers/uaccess: add a workaround for Intel's SMAP feature

PATCH New Xiaoguang Wang 2 participants 4 messages Mar 15, 2016

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Xiaoguang Wang

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#0 lore raw

PATCH 1/1 device-drivers/uaccess: add a workaround for Intel's SMAP feature

When Intel's new "Supervisor Mode Access Prevention" (SMAP) feature is enabled, kernel will be forbidden to visit user space memory, please see url: https://lwn.net/Articles/517475/ for detailed infomation.

Here, we explicitly call stac()/clac() to enable/disable SMAP feature.

Signed-off-by Xiaoguang Wang <[email protected]>
---
 testcases/kernel/device-drivers/uaccess/ltp_uaccess.c | 8 ++++++++
 1 file changed, 8 insertions(+)
testcases/kernel/device-drivers/uaccess/ltp_uaccess.c +8 -0
index a9a06e9..35a9aa0 100644
@@ -68,6 +68,9 @@ static ssize_t sys_tcase(struct device *dev,
 	str = (char *) ptr;
 	test_result = 0;
 
+#ifdef CONFIG_X86_SMAP
+	stac();
+#endif
 	switch (tc) {
 	case TC_READ_USER:
 		if (copy_from_user(buffer, str, str_size))

@@ -90,6 +93,11 @@ static ssize_t sys_tcase(struct device *dev,
 	break;
 	}
 
+#ifdef CONFIG_X86_SMAP
+	clac();
+#endif
+
+
 	return count;
 }
 static DEVICE_ATTR(tcase, S_IWUSR, NULL, sys_tcase);
Signature · 1 line
1.8.3.1
author
#1 lore raw

PATCH 1/1 device-drivers/uaccess: add a workaround for Intel's SMAP feature

hello,

Sorry, I do not have a machine with this SMAP feature, anybody can help to test this patch, thanks very much.

Regards,
Xiaoguang Wang

Quoted 38 lines · Xiaoguang Wang

When Intel's new "Supervisor Mode Access Prevention" (SMAP) feature is enabled, kernel will be forbidden to visit user space memory, please see url: https://lwn.net/Articles/517475/ for detailed infomation.

Here, we explicitly call stac()/clac() to enable/disable SMAP feature.

Signed-off-by Xiaoguang Wang <[email protected]>
---
 testcases/kernel/device-drivers/uaccess/ltp_uaccess.c | 8 ++++++++
 1 file changed, 8 insertions(+)
testcases/kernel/device-drivers/uaccess/ltp_uaccess.c +8 -0
index a9a06e9..35a9aa0 100644
@@ -68,6 +68,9 @@ static ssize_t sys_tcase(struct device *dev,
 	str = (char *) ptr;
 	test_result = 0;
 
+#ifdef CONFIG_X86_SMAP
+	stac();
+#endif
 	switch (tc) {
 	case TC_READ_USER:
 		if (copy_from_user(buffer, str, str_size))

@@ -90,6 +93,11 @@ static ssize_t sys_tcase(struct device *dev,
 	break;
 	}
 
+#ifdef CONFIG_X86_SMAP
+	clac();
+#endif
+
+
 	return count;
 }
 static DEVICE_ATTR(tcase, S_IWUSR, NULL, sys_tcase);
#2 lore raw

PATCH 1/1 device-drivers/uaccess: add a workaround for Intel's SMAP feature

Hi,

Quoted 38 lines · Xiaoguang Wang

hello,

Sorry, I do not have a machine with this SMAP feature, anybody can help to test this patch, thanks very much.

Regards,
Xiaoguang Wang

Quoted 29 lines · Xiaoguang Wang

When Intel's new "Supervisor Mode Access Prevention" (SMAP) feature is enabled, kernel will be forbidden to visit user space memory, please see url: https://lwn.net/Articles/517475/ for detailed infomation.

Here, we explicitly call stac()/clac() to enable/disable SMAP feature.

Signed-off-by Xiaoguang Wang <[email protected]>
---
  testcases/kernel/device-drivers/uaccess/ltp_uaccess.c | 8 ++++++++
  1 file changed, 8 insertions(+)
testcases/kernel/device-drivers/uaccess/ltp_uaccess.c +3 -0
index a9a06e9..35a9aa0 100644
@@ -68,6 +68,9 @@ static ssize_t sys_tcase(struct device *dev,
  	str = (char *) ptr;
  	test_result = 0;
 
+#ifdef CONFIG_X86_SMAP
+	stac();
+#endif
  	switch (tc) {
  	case TC_READ_USER:
  		if (copy_from_user(buffer, str, str_size))

@@ -90,6 +93,11 @@ static ssize_t sys_tcase(struct device *dev,
  	break;
  	}
Quoted 3 lines

testcases/kernel/device-drivers/uaccess/ltp_uaccess.c static ssize_t sys_tcase(struct device *dev, · line 98

Quoted 3 lines
testcases/kernel/device-drivers/uaccess/ltp_uaccess.c +3 -0
+#ifdef CONFIG_X86_SMAP
+	clac();
+#endif

copy_from_user() and others have stac() / clac() already. Are you sure we need to invoke them there again?

Thanks,
Alexey

#3 lore raw

PATCH 1/1 device-drivers/uaccess: add a workaround for Intel's SMAP feature

Quoted 22 lines · Alexey Kodanev

Hi,

Quoted 20 lines · Xiaoguang Wang

hello,

Sorry, I do not have a machine with this SMAP feature, anybody can help to test this patch, thanks very much.

Regards,
Xiaoguang Wang

Quoted 11 lines · Xiaoguang Wang

When Intel's new "Supervisor Mode Access Prevention" (SMAP) feature is enabled, kernel will be forbidden to visit user space memory, please see url: https://lwn.net/Articles/517475/ for detailed infomation.

Here, we explicitly call stac()/clac() to enable/disable SMAP feature.

Signed-off-by Xiaoguang Wang <[email protected]>

---
testcases/kernel/device-drivers/uaccess/ltp_uaccess.c | 8 ++++++++

  1 file changed, 8 insertions(+)
Quoted 11 lines
Quoted 11 lines

testcases/kernel/device-drivers/uaccess/ltp_uaccess.c static ssize_t sys_tcase(struct device *dev, · line 72

Quoted 11 lines
testcases/kernel/device-drivers/uaccess/ltp_uaccess.c +2 -0
index a9a06e9..35a9aa0 100644
@@ -68,6 +68,9 @@ static ssize_t sys_tcase(struct device *dev,
      str = (char *) ptr;
      test_result = 0;
  +#ifdef CONFIG_X86_SMAP
+    stac();
+#endif

Also you don't need ifdefs as smap.h has a check:

...
#else /* CONFIG_X86_SMAP */

static inline void clac(void) { }
static inline void stac(void) { }
...

Quoted 19 lines
Quoted 10 lines

testcases/kernel/device-drivers/uaccess/ltp_uaccess.c static ssize_t sys_tcase(struct device *dev, · line 97

Quoted 10 lines
testcases/kernel/device-drivers/uaccess/ltp_uaccess.c +2 -0
      switch (tc) {
      case TC_READ_USER:
          if (copy_from_user(buffer, str, str_size))

@@ -90,6 +93,11 @@ static ssize_t sys_tcase(struct device *dev,
      break;
      }
  +#ifdef CONFIG_X86_SMAP
+    clac();
+#endif

copy_from_user() and others have stac() / clac() already. Are you sure we need to invoke them there again?

Thanks,
Alexey