Commit c6c9645e authored by Christopher M. Riedl's avatar Christopher M. Riedl Committed by Michael Ellerman
Browse files

powerpc/signal64: Remove non-inline calls from setup_sigcontext() 



The majority of setup_sigcontext() can be refactored to execute in an
"unsafe" context assuming an open uaccess window except for some
non-inline function calls. Move these out into a separate
prepare_setup_sigcontext() function which must be called first and
before opening up a uaccess window. Non-inline function calls should be
avoided during a uaccess window for a few reasons:

	- KUAP should be enabled for as much kernel code as possible.
	  Opening a uaccess window disables KUAP which means any code
	  executed during this time contributes to a potential attack
	  surface.

	- Non-inline functions default to traceable which means they are
	  instrumented for ftrace. This adds more code which could run
	  with KUAP disabled.

	- Powerpc does not currently support the objtool UACCESS checks.
	  All code running with uaccess must be audited manually which
	  means: less code -> less work -> fewer problems (in theory).

A follow-up commit converts setup_sigcontext() to be "unsafe".

Signed-off-by: default avatarChristopher M. Riedl <cmr@codefail.de>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210227011259.11992-4-cmr@codefail.de
parent 609355df

arch/powerpc/kernel/signal_64.c

+21 −11
Original line number Diff line number Diff line
@@ -79,6 +79,24 @@ static elf_vrreg_t __user *sigcontext_vmx_regs(struct sigcontext __user *sc) 
}

#endif



static void prepare_setup_sigcontext(struct task_struct *tsk)

{

#ifdef CONFIG_ALTIVEC

	/* save altivec registers */

	if (tsk->thread.used_vr)

		flush_altivec_to_thread(tsk);

	if (cpu_has_feature(CPU_FTR_ALTIVEC))

		tsk->thread.vrsave = mfspr(SPRN_VRSAVE);

#endif /* CONFIG_ALTIVEC */



	flush_fp_to_thread(tsk);



#ifdef CONFIG_VSX

	if (tsk->thread.used_vsr)

		flush_vsx_to_thread(tsk);

#endif /* CONFIG_VSX */

}



/*

 * Set up the sigcontext for the signal frame.

 */
@@ -97,7 +115,6 @@ static long setup_sigcontext(struct sigcontext __user *sc, 
	 */

#ifdef CONFIG_ALTIVEC

	elf_vrreg_t __user *v_regs = sigcontext_vmx_regs(sc);

	unsigned long vrsave;

#endif

	struct pt_regs *regs = tsk->thread.regs;

	unsigned long msr = regs->msr;
@@ -112,7 +129,6 @@ static long setup_sigcontext(struct sigcontext __user *sc, 


	/* save altivec registers */

	if (tsk->thread.used_vr) {

		flush_altivec_to_thread(tsk);

		/* Copy 33 vec registers (vr0..31 and vscr) to the stack */

		err |= __copy_to_user(v_regs, &tsk->thread.vr_state,

				      33 * sizeof(vector128));
@@ -124,17 +140,10 @@ static long setup_sigcontext(struct sigcontext __user *sc, 
	/* We always copy to/from vrsave, it's 0 if we don't have or don't

	 * use altivec.

	 */

	vrsave = 0;

	if (cpu_has_feature(CPU_FTR_ALTIVEC)) {

		vrsave = mfspr(SPRN_VRSAVE);

		tsk->thread.vrsave = vrsave;

	}



	err |= __put_user(vrsave, (u32 __user *)&v_regs[33]);

	err |= __put_user(tsk->thread.vrsave, (u32 __user *)&v_regs[33]);

#else /* CONFIG_ALTIVEC */

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

#endif /* CONFIG_ALTIVEC */

	flush_fp_to_thread(tsk);

	/* copy fpr regs and fpscr */

	err |= copy_fpr_to_user(&sc->fp_regs, tsk);
@@ -150,7 +159,6 @@ static long setup_sigcontext(struct sigcontext __user *sc, 
	 * VMX data.

	 */

	if (tsk->thread.used_vsr && ctx_has_vsx_region) {

		flush_vsx_to_thread(tsk);

		v_regs += ELF_NVRREG;

		err |= copy_vsx_to_user(v_regs, tsk);

		/* set MSR_VSX in the MSR value in the frame to
@@ -655,6 +663,7 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext __user *, old_ctx, 
		ctx_has_vsx_region = 1;



	if (old_ctx != NULL) {

		prepare_setup_sigcontext(current);

		if (!access_ok(old_ctx, ctx_size)

		    || setup_sigcontext(&old_ctx->uc_mcontext, current, 0, NULL, 0,

					ctx_has_vsx_region)
@@ -842,6 +851,7 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set, 
#endif

	{

		err |= __put_user(0, &frame->uc.uc_link);

		prepare_setup_sigcontext(tsk);

		err |= setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,

					NULL, (unsigned long)ksig->ka.sa.sa_handler,

					1);