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um: allocate a guard page to helper threads

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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>
This commit is contained in:
Johannes Berg
2020-12-05 21:50:18 +01:00
committed by Richard Weinberger
parent 963285b0b4
commit ef4459a6da
4 changed files with 11 additions and 8 deletions
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11
arch/um/kernel/process.c
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@@ -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)