Commit ef4459a6 authored by Johannes Berg's avatar Johannes Berg Committed by Richard Weinberger
Browse files

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: default avatarJohannes Berg <johannes.berg@intel.com>
Signed-off-by: default avatarRichard Weinberger <richard@nod.at>
parent 963285b0

arch/um/drivers/ubd_kern.c

+1 −1
Original line number Diff line number Diff line
@@ -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){

arch/um/include/shared/kern_util.h

+1 −1
Original line number Diff line number Diff line
@@ -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;

arch/um/kernel/process.c

+7 −4
Original line number Diff line number Diff line
@@ -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)

arch/um/os-Linux/helper.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

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