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authorJohannes Berg <johannes.berg@intel.com>2020-12-05 21:50:18 +0100
committerRichard Weinberger <richard@nod.at>2020-12-13 22:38:06 +0100
commitef4459a6da0955b533ebfc97a7d756ac090f50c9 (patch)
tree5c1153080467c99b2f60942757f644d38338319b
parent963285b0b47a1b8e1dfa5481717855a7057ccec6 (diff)
um: allocate a guard page to helper threads
We've been running into stack overflows in helper threads corrupting memory (e.g. because somebody put printf() or os_info() there), so to avoid those causing hard-to-debug issues later on, allocate a guard page for helper thread stacks and mark it read-only. Unfortunately, the crash dump at that point is useless as the stack tracer will try to backtrace the *kernel* thread, not the helper thread, but at least we don't survive to a random issue caused by corruption. Signed-off-by: Johannes Berg <johannes.berg@intel.com> Signed-off-by: Richard Weinberger <richard@nod.at>
-rw-r--r--arch/um/drivers/ubd_kern.c2
-rw-r--r--arch/um/include/shared/kern_util.h2
-rw-r--r--arch/um/kernel/process.c11
-rw-r--r--arch/um/os-Linux/helper.c4
4 files changed, 11 insertions, 8 deletions
diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 7e07b321e847..13b1fe694b90 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -1241,7 +1241,7 @@ static int __init ubd_driver_init(void){
/* Letting ubd=sync be like using ubd#s= instead of ubd#= is
* enough. So use anyway the io thread. */
}
- stack = alloc_stack(0, 0);
+ stack = alloc_stack(0);
io_pid = start_io_thread(stack + PAGE_SIZE - sizeof(void *),
&thread_fd);
if(io_pid < 0){
diff --git a/arch/um/include/shared/kern_util.h b/arch/um/include/shared/kern_util.h
index 2888ec812f6e..d8c279e3312f 100644
--- a/arch/um/include/shared/kern_util.h
+++ b/arch/um/include/shared/kern_util.h
@@ -19,7 +19,7 @@ extern int kmalloc_ok;
#define UML_ROUND_UP(addr) \
((((unsigned long) addr) + PAGE_SIZE - 1) & PAGE_MASK)
-extern unsigned long alloc_stack(int order, int atomic);
+extern unsigned long alloc_stack(int atomic);
extern void free_stack(unsigned long stack, int order);
struct pt_regs;
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index 81d508daf67c..2a986ece5478 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -32,6 +32,7 @@
#include <os.h>
#include <skas.h>
#include <linux/time-internal.h>
+#include <asm/set_memory.h>
/*
* This is a per-cpu array. A processor only modifies its entry and it only
@@ -62,16 +63,18 @@ void free_stack(unsigned long stack, int order)
free_pages(stack, order);
}
-unsigned long alloc_stack(int order, int atomic)
+unsigned long alloc_stack(int atomic)
{
- unsigned long page;
+ unsigned long addr;
gfp_t flags = GFP_KERNEL;
if (atomic)
flags = GFP_ATOMIC;
- page = __get_free_pages(flags, order);
+ addr = __get_free_pages(flags, 1);
- return page;
+ set_memory_ro(addr, 1);
+
+ return addr + PAGE_SIZE;
}
static inline void set_current(struct task_struct *task)
diff --git a/arch/um/os-Linux/helper.c b/arch/um/os-Linux/helper.c
index 9fa6e4187d4f..feb48d796e00 100644
--- a/arch/um/os-Linux/helper.c
+++ b/arch/um/os-Linux/helper.c
@@ -45,7 +45,7 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv)
unsigned long stack, sp;
int pid, fds[2], ret, n;
- stack = alloc_stack(0, __cant_sleep());
+ stack = alloc_stack(__cant_sleep());
if (stack == 0)
return -ENOMEM;
@@ -116,7 +116,7 @@ int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
unsigned long stack, sp;
int pid, status, err;
- stack = alloc_stack(0, __cant_sleep());
+ stack = alloc_stack(__cant_sleep());
if (stack == 0)
return -ENOMEM;