x86/elf/64: Clear more registers in elf_common_init()

Before we start calling execve in contexts that honor the full
pt_regs, we need to teach it to initialize all registers.

Signed-off-by: Andy Lutomirski <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: Denys Vlasenko <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/include/asm/elf.h

···
 static inline void elf_common_init(struct thread_struct *t,
 				   struct pt_regs *regs, const u16 ds)
 {
-	/* Commented-out registers are cleared in stub_execve */
-	/*regs->ax = regs->bx =*/ regs->cx = regs->dx = 0;
-	regs->si = regs->di /*= regs->bp*/ = 0;
+	/* ax gets execve's return value. */
+	/*regs->ax = */ regs->bx = regs->cx = regs->dx = 0;
+	regs->si = regs->di = regs->bp = 0;
 	regs->r8 = regs->r9 = regs->r10 = regs->r11 = 0;
-	/*regs->r12 = regs->r13 = regs->r14 = regs->r15 = 0;*/
+	regs->r12 = regs->r13 = regs->r14 = regs->r15 = 0;
 	t->fs = t->gs = 0;
 	t->fsindex = t->gsindex = 0;
 	t->ds = t->es = ds;