um: Implement probe_kernel_read()
UML needs it's own probe_kernel_read() to handle kernel
mode faults correctly.
The implementation uses mincore() on the host side to detect
whether a page is owned by the UML kernel process.
This fixes also a possible crash when sysrq-t is used.
Starting with 3.10 sysrq-t calls probe_kernel_read() to
read details from the kernel workers. As kernel worker are
completely async pointers may turn NULL while reading them.
Cc: <stian@nixia.no>
Cc: <tj@kernel.org>
Cc: <stable@vger.kernel.org> # 3.10.x
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
index b8f34c9..67b9c8f 100644
--- a/arch/um/os-Linux/process.c
+++ b/arch/um/os-Linux/process.c
@@ -4,6 +4,7 @@
*/
#include <stdio.h>
+#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
@@ -232,6 +233,57 @@
return ok;
}
+static int os_page_mincore(void *addr)
+{
+ char vec[2];
+ int ret;
+
+ ret = mincore(addr, UM_KERN_PAGE_SIZE, vec);
+ if (ret < 0) {
+ if (errno == ENOMEM || errno == EINVAL)
+ return 0;
+ else
+ return -errno;
+ }
+
+ return vec[0] & 1;
+}
+
+int os_mincore(void *addr, unsigned long len)
+{
+ char *vec;
+ int ret, i;
+
+ if (len <= UM_KERN_PAGE_SIZE)
+ return os_page_mincore(addr);
+
+ vec = calloc(1, (len + UM_KERN_PAGE_SIZE - 1) / UM_KERN_PAGE_SIZE);
+ if (!vec)
+ return -ENOMEM;
+
+ ret = mincore(addr, UM_KERN_PAGE_SIZE, vec);
+ if (ret < 0) {
+ if (errno == ENOMEM || errno == EINVAL)
+ ret = 0;
+ else
+ ret = -errno;
+
+ goto out;
+ }
+
+ for (i = 0; i < ((len + UM_KERN_PAGE_SIZE - 1) / UM_KERN_PAGE_SIZE); i++) {
+ if (!(vec[i] & 1)) {
+ ret = 0;
+ goto out;
+ }
+ }
+
+ ret = 1;
+out:
+ free(vec);
+ return ret;
+}
+
void init_new_thread_signals(void)
{
set_handler(SIGSEGV);