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-rw-r--r--arch/x86/kernel/ptrace.c30
1 files changed, 30 insertions, 0 deletions
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index b00b33a18390..5e0596b0632e 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -22,6 +22,7 @@
#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>
#include <linux/rcupdate.h>
+#include <linux/module.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
@@ -166,6 +167,35 @@ static inline bool invalid_selector(u16 value)
#define FLAG_MASK FLAG_MASK_32
+/*
+ * X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode
+ * when it traps. The previous stack will be directly underneath the saved
+ * registers, and 'sp/ss' won't even have been saved. Thus the '&regs->sp'.
+ *
+ * Now, if the stack is empty, '&regs->sp' is out of range. In this
+ * case we try to take the previous stack. To always return a non-null
+ * stack pointer we fall back to regs as stack if no previous stack
+ * exists.
+ *
+ * This is valid only for kernel mode traps.
+ */
+unsigned long kernel_stack_pointer(struct pt_regs *regs)
+{
+ unsigned long context = (unsigned long)regs & ~(THREAD_SIZE - 1);
+ unsigned long sp = (unsigned long)&regs->sp;
+ struct thread_info *tinfo;
+
+ if (context == (sp & ~(THREAD_SIZE - 1)))
+ return sp;
+
+ tinfo = (struct thread_info *)context;
+ if (tinfo->previous_esp)
+ return tinfo->previous_esp;
+
+ return (unsigned long)regs;
+}
+EXPORT_SYMBOL_GPL(kernel_stack_pointer);
+
static unsigned long *pt_regs_access(struct pt_regs *regs, unsigned long regno)
{
BUILD_BUG_ON(offsetof(struct pt_regs, bx) != 0);