This is a note to let you know that I've just added the patch titled
alpha: fix FEN fault handling
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
alpha-fix-fen-fault-handling.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 977a3009547dad4a5bc95d91be4a58c9f7eedac0 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Fri, 6 Jan 2023 19:25:59 -0500
Subject: alpha: fix FEN fault handling
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
commit 977a3009547dad4a5bc95d91be4a58c9f7eedac0 upstream.
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@xxxxxxxxxxxxxxx
Reviewed-by: Richard Henderson <rth@xxxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/alpha/kernel/traps.c | 30 +++++++++++++++---------------
1 file changed, 15 insertions(+), 15 deletions(-)
--- a/arch/alpha/kernel/traps.c
+++ b/arch/alpha/kernel/traps.c
@@ -235,7 +235,21 @@ do_entIF(unsigned long type, struct pt_r
{
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(¤t_thread_info()->pcb);
+ return;
+ }
+ if (!user_mode(regs)) {
if (type == 1) {
const unsigned int *data
= (const unsigned int *) regs->pc;
@@ -368,20 +382,6 @@ do_entIF(unsigned long type, struct pt_r
}
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(¤t_thread_info()->pcb);
- return;
-
case 5: /* illoc */
default: /* unexpected instruction-fault type */
;
Patches currently in stable-queue which might be from viro@xxxxxxxxxxxxxxxxxx are
queue-5.10/alpha-boot-tools-objstrip-fix-the-check-for-elf-head.patch
queue-5.10/alpha-fix-fen-fault-handling.patch
