Commit e4e5d324 authored by Bryan Ford's avatar Bryan Ford Committed by Linus Torvalds
Browse files

[PATCH] x86_64: Save/restore CS in 64bit signal handlers and force __USER_CS for CS 



This allows to run 64bit signal handlers in 64bit processes that run small
code snippets in compat mode.

Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 420f8f68

arch/x86_64/kernel/signal.c

+17 −0
Original line number Diff line number Diff line
@@ -110,6 +110,15 @@ restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc, unsigned 
	COPY(r14);

	COPY(r15);



	/* Kernel saves and restores only the CS segment register on signals,

	 * which is the bare minimum needed to allow mixed 32/64-bit code.

	 * App's signal handler can save/restore other segments if needed. */

	{

		unsigned cs;

		err |= __get_user(cs, &sc->cs);

		regs->cs = cs | 3;	/* Force into user mode */

	}



	{

		unsigned int tmpflags;

		err |= __get_user(tmpflags, &sc->eflags);
@@ -187,6 +196,7 @@ setup_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs, unsigned lo 
{

	int err = 0;



	err |= __put_user(regs->cs, &sc->cs);

	err |= __put_user(0, &sc->gs);

	err |= __put_user(0, &sc->fs);
@@ -318,7 +328,14 @@ static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info, 


	regs->rsp = (unsigned long)frame;



	/* Set up the CS register to run signal handlers in 64-bit mode,

	   even if the handler happens to be interrupting 32-bit code. */

	regs->cs = __USER_CS;



	/* This, by contrast, has nothing to do with segment registers -

	   see include/asm-x86_64/uaccess.h for details. */

	set_fs(USER_DS);



	regs->eflags &= ~TF_MASK;

	if (test_thread_flag(TIF_SINGLESTEP))

		ptrace_notify(SIGTRAP);