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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: Christopher M. Riedl <cmr@codefail.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210227011259.11992-4-cmr@codefail.de
This commit is contained in:
Christopher M. Riedl 2021-02-26 19:12:52 -06:00 committed by Michael Ellerman
parent 609355dfc8
commit c6c9645e37
1 changed files with 21 additions and 11 deletions
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32
arch/powerpc/kernel/signal_64.c
View File

@ -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);