Commit 977a3009 authored by Al Viro's avatar Al Viro

alpha: fix FEN fault handling

Type 3 instruction fault (FPU insn with FPU disabled) is handled
by quietly enabling FPU and returning.  Which is fine, except that
we need to do that both for fault in userland and in the kernel;
the latter *can* legitimately happen - all it takes is this:

.global _start
_start:
        call_pal 0xae
	lda $0, 0
	ldq $0, 0($0)

- call_pal CLRFEN to clear "FPU enabled" flag and arrange for
a signal delivery (SIGSEGV in this case).

Fixed by moving the handling of type 3 into the common part of
do_entIF(), before we check for kernel vs. user mode.

Incidentally, the check for kernel mode is unidiomatic; the normal
way to do that is !user_mode(regs).  The difference is that
the open-coded variant treats any of bits 63..3 of regs->ps being
set as "it's user mode" while the normal approach is to check just
the bit 3.  PS is a 4-bit register and regs->ps always will have
bits 63..4 clear, so the open-coded variant here is actually equivalent
to !user_mode(regs).  Harder to follow, though...

Cc: stable@vger.kernel.org
Reviewed-by: default avatarRichard Henderson <rth@twiddle.net>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent b7bfaa76
...@@ -233,7 +233,21 @@ do_entIF(unsigned long type, struct pt_regs *regs) ...@@ -233,7 +233,21 @@ do_entIF(unsigned long type, struct pt_regs *regs)
{ {
int signo, code; int signo, code;
if ((regs->ps & ~IPL_MAX) == 0) { if (type == 3) { /* FEN fault */
/* Irritating users can call PAL_clrfen to disable the
FPU for the process. The kernel will then trap in
do_switch_stack and undo_switch_stack when we try
to save and restore the FP registers.
Given that GCC by default generates code that uses the
FP registers, PAL_clrfen is not useful except for DoS
attacks. So turn the bleeding FPU back on and be done
with it. */
current_thread_info()->pcb.flags |= 1;
__reload_thread(&current_thread_info()->pcb);
return;
}
if (!user_mode(regs)) {
if (type == 1) { if (type == 1) {
const unsigned int *data const unsigned int *data
= (const unsigned int *) regs->pc; = (const unsigned int *) regs->pc;
...@@ -366,20 +380,6 @@ do_entIF(unsigned long type, struct pt_regs *regs) ...@@ -366,20 +380,6 @@ do_entIF(unsigned long type, struct pt_regs *regs)
} }
break; break;
case 3: /* FEN fault */
/* Irritating users can call PAL_clrfen to disable the
FPU for the process. The kernel will then trap in
do_switch_stack and undo_switch_stack when we try
to save and restore the FP registers.
Given that GCC by default generates code that uses the
FP registers, PAL_clrfen is not useful except for DoS
attacks. So turn the bleeding FPU back on and be done
with it. */
current_thread_info()->pcb.flags |= 1;
__reload_thread(&current_thread_info()->pcb);
return;
case 5: /* illoc */ case 5: /* illoc */
default: /* unexpected instruction-fault type */ default: /* unexpected instruction-fault type */
; ;
......
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