x86/entry: Add do_syscall_32(), a C function to do 32-bit syscalls

System calls are really quite simple.  Add a helper to call
a 32-bit system call.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/a77ed179834c27da436fb4a7fb23c8ee77abc11c.1444091585.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index d94a60c160293577a5f9fd724159b7b756513769..41d17508cf461625add3cf74474eea5fcd57a51e 100644 (file)
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -318,3 +318,46 @@ __visible void syscall_return_slowpath(struct pt_regs *regs)
        local_irq_disable();
        prepare_exit_to_usermode(regs);
 }
+
+#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
+/*
+ * Does a 32-bit syscall.  Called with IRQs off and does all entry and
+ * exit work.
+ */
+__visible void do_int80_syscall_32(struct pt_regs *regs)
+{
+       struct thread_info *ti = pt_regs_to_thread_info(regs);
+       unsigned int nr = (unsigned int)regs->orig_ax;
+
+#ifdef CONFIG_IA32_EMULATION
+       ti->status |= TS_COMPAT;
+#endif
+
+       local_irq_enable();
+
+       if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
+               /*
+                * Subtlety here: if ptrace pokes something larger than
+                * 2^32-1 into orig_ax, this truncates it.  This may or
+                * may not be necessary, but it matches the old asm
+                * behavior.
+                */
+               nr = syscall_trace_enter(regs);
+       }
+
+       if (nr < IA32_NR_syscalls) {
+               /*
+                * It's possible that a 32-bit syscall implementation
+                * takes a 64-bit parameter but nonetheless assumes that
+                * the high bits are zero.  Make sure we zero-extend all
+                * of the args.
+                */
+               regs->ax = ia32_sys_call_table[nr](
+                       (unsigned int)regs->bx, (unsigned int)regs->cx,
+                       (unsigned int)regs->dx, (unsigned int)regs->si,
+                       (unsigned int)regs->di, (unsigned int)regs->bp);
+       }
+
+       syscall_return_slowpath(regs);
+}
+#endif