MFC r258135: x86: Allow users to change PSL_RF via ptrace(PT_SETREGS...)

  Debuggers may need to change PSL_RF. Note that tf_eflags is already stored
  in the signal context during signal handling and PSL_RF previously could
  be modified via sigreturn, so this change should not provide any new
  ability to userspace.

  For background see the thread at:
  http://lists.freebsd.org/pipermail/freebsd-i386/2007-September/005910.html

  Reviewed by:	jhb, kib

Sponsored by:	DARPA, AFRL
Approved by:	re (gjb)

1 files changed, 3 insertions, 33 deletions

diff --git a/sys/pc98/pc98/machdep.c b/sys/pc98/pc98/machdep.c
index 4435186..a4887c6 100644
--- a/sys/pc98/pc98/machdep.c
+++ b/sys/pc98/pc98/machdep.c
@@ -773,17 +773,7 @@ osigreturn(td, uap)
 		/*
 		 * Don't allow users to change privileged or reserved flags.
 		 */
-		/*
-		 * XXX do allow users to change the privileged flag PSL_RF.
-		 * The cpu sets PSL_RF in tf_eflags for faults.  Debuggers
-		 * should sometimes set it there too.  tf_eflags is kept in
-		 * the signal context during signal handling and there is no
-		 * other place to remember it, so the PSL_RF bit may be
-		 * corrupted by the signal handler without us knowing.
-		 * Corruption of the PSL_RF bit at worst causes one more or
-		 * one less debugger trap, so allowing it is fairly harmless.
-		 */
-		if (!EFL_SECURE(eflags & ~PSL_RF, regs->tf_eflags & ~PSL_RF)) {
+		if (!EFL_SECURE(eflags, regs->tf_eflags)) {
 	    		return (EINVAL);
 		}
 
@@ -899,17 +889,7 @@ freebsd4_sigreturn(td, uap)
 		/*
 		 * Don't allow users to change privileged or reserved flags.
 		 */
-		/*
-		 * XXX do allow users to change the privileged flag PSL_RF.
-		 * The cpu sets PSL_RF in tf_eflags for faults.  Debuggers
-		 * should sometimes set it there too.  tf_eflags is kept in
-		 * the signal context during signal handling and there is no
-		 * other place to remember it, so the PSL_RF bit may be
-		 * corrupted by the signal handler without us knowing.
-		 * Corruption of the PSL_RF bit at worst causes one more or
-		 * one less debugger trap, so allowing it is fairly harmless.
-		 */
-		if (!EFL_SECURE(eflags & ~PSL_RF, regs->tf_eflags & ~PSL_RF)) {
+		if (!EFL_SECURE(eflags, regs->tf_eflags)) {
 			uprintf("pid %d (%s): freebsd4_sigreturn eflags = 0x%x\n",
 			    td->td_proc->p_pid, td->td_name, eflags);
 	    		return (EINVAL);
@@ -1013,17 +993,7 @@ sys_sigreturn(td, uap)
 		/*
 		 * Don't allow users to change privileged or reserved flags.
 		 */
-		/*
-		 * XXX do allow users to change the privileged flag PSL_RF.
-		 * The cpu sets PSL_RF in tf_eflags for faults.  Debuggers
-		 * should sometimes set it there too.  tf_eflags is kept in
-		 * the signal context during signal handling and there is no
-		 * other place to remember it, so the PSL_RF bit may be
-		 * corrupted by the signal handler without us knowing.
-		 * Corruption of the PSL_RF bit at worst causes one more or
-		 * one less debugger trap, so allowing it is fairly harmless.
-		 */
-		if (!EFL_SECURE(eflags & ~PSL_RF, regs->tf_eflags & ~PSL_RF)) {
+		if (!EFL_SECURE(eflags, regs->tf_eflags)) {
 			uprintf("pid %d (%s): sigreturn eflags = 0x%x\n",
 			    td->td_proc->p_pid, td->td_name, eflags);
 	    		return (EINVAL);