From bf5147c58bc1794538a7c6cf30b6f8801c9e96d9 Mon Sep 17 00:00:00 2001 From: John Baldwin Date: Thu, 10 Oct 2013 19:51:38 +0000 Subject: [PATCH] Sanitize the %eflags returned by BIOS routines. Some BIOS routines enter protected mode and may leave protected-mode-specific flags like PSL_NT set when they return to real mode. This can cause a fault when BTX re-enters protected mode after the BIOS mode returns. PR: amd64/182740 Reported by: Julian Pidancet Approved by: re (gjb) MFC after: 1 week --- sys/boot/i386/btx/btx/btx.S | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/sys/boot/i386/btx/btx/btx.S b/sys/boot/i386/btx/btx/btx.S index ef3d0c763b9b..87d09a5a1e17 100644 --- a/sys/boot/i386/btx/btx/btx.S +++ b/sys/boot/i386/btx/btx/btx.S @@ -41,6 +41,8 @@ .set PSL_RESERVED_DEFAULT,0x00000002 .set PSL_T,0x00000100 # Trap flag .set PSL_I,0x00000200 # Interrupt enable flag + .set PSL_D,0x00000400 # String instruction direction + .set PSL_NT,0x00004000 # Nested task flag .set PSL_VM,0x00020000 # Virtual 8086 mode flag .set PSL_AC,0x00040000 # Alignment check flag /* @@ -611,8 +613,8 @@ rret_tramp: movw $MEM_ESPR-0x08,%sp # Reset stack pointer pushl %ds # regs pushl %es pushfl # Save %eflags - cli # Disable interrupts - std # String ops dec + pushl $PSL_RESERVED_DEFAULT|PSL_D # Use clean %eflags with + popfl # string ops dec xorw %ax,%ax # Reset seg movw %ax,%ds # regs movw %ax,%es # (%ss is already 0) @@ -675,6 +677,7 @@ rret_tramp.1: xorl %ecx,%ecx # Zero testl $V86F_FLAGS,%edx # User wants flags? jz rret_tramp.3 # No movl MEM_ESPR-0x3c,%eax # Read real mode flags + andl $~(PSL_T|PSL_NT),%eax # Clear unsafe flags movw %ax,-0x08(%esi) # Update user flags (low 16) /* * Return to the user task