[3.13.y.z extended stable] Patch "x86, espfix: Make it possible to disable 16-bit support" has been added to staging queue
Kamal Mostafa
kamal at canonical.com
Tue Sep 2 21:37:12 UTC 2014
This is a note to let you know that I have just added a patch titled
x86, espfix: Make it possible to disable 16-bit support
to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree
which can be found at:
http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue
This patch is scheduled to be released in version 3.13.11.7.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
------
>From 8afe71feb2dc17b15f14ce936189e5238b99b016 Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <hpa at zytor.com>
Date: Sun, 4 May 2014 10:36:22 -0700
Subject: x86, espfix: Make it possible to disable 16-bit support
commit 34273f41d57ee8d854dcd2a1d754cbb546cb548f upstream.
Embedded systems, which may be very memory-size-sensitive, are
extremely unlikely to ever encounter any 16-bit software, so make it
a CONFIG_EXPERT option to turn off support for any 16-bit software
whatsoever.
Signed-off-by: H. Peter Anvin <hpa at zytor.com>
Link: http://lkml.kernel.org/r/1398816946-3351-1-git-send-email-hpa@linux.intel.com
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
arch/x86/Kconfig | 23 ++++++++++++++++++-----
arch/x86/kernel/entry_32.S | 12 ++++++++++++
arch/x86/kernel/entry_64.S | 8 ++++++++
arch/x86/kernel/ldt.c | 5 +++++
4 files changed, 43 insertions(+), 5 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ea1c3af..08fa7df 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -978,14 +978,27 @@ config VM86
default y
depends on X86_32
---help---
- This option is required by programs like DOSEMU to run 16-bit legacy
- code on X86 processors. It also may be needed by software like
- XFree86 to initialize some video cards via BIOS. Disabling this
- option saves about 6k.
+ This option is required by programs like DOSEMU to run
+ 16-bit real mode legacy code on x86 processors. It also may
+ be needed by software like XFree86 to initialize some video
+ cards via BIOS. Disabling this option saves about 6K.
+
+config X86_16BIT
+ bool "Enable support for 16-bit segments" if EXPERT
+ default y
+ ---help---
+ This option is required by programs like Wine to run 16-bit
+ protected mode legacy code on x86 processors. Disabling
+ this option saves about 300 bytes on i386, or around 6K text
+ plus 16K runtime memory on x86-64,
+
+config X86_ESPFIX32
+ def_bool y
+ depends on X86_16BIT && X86_32
config X86_ESPFIX64
def_bool y
- depends on X86_64
+ depends on X86_16BIT && X86_64
config TOSHIBA
tristate "Toshiba Laptop support"
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index c87810b..c5a9cb9 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -529,6 +529,7 @@ syscall_exit:
restore_all:
TRACE_IRQS_IRET
restore_all_notrace:
+#ifdef CONFIG_X86_ESPFIX32
movl PT_EFLAGS(%esp), %eax # mix EFLAGS, SS and CS
# Warning: PT_OLDSS(%esp) contains the wrong/random values if we
# are returning to the kernel.
@@ -539,6 +540,7 @@ restore_all_notrace:
cmpl $((SEGMENT_LDT << 8) | USER_RPL), %eax
CFI_REMEMBER_STATE
je ldt_ss # returning to user-space with LDT SS
+#endif
restore_nocheck:
RESTORE_REGS 4 # skip orig_eax/error_code
irq_return:
@@ -551,6 +553,7 @@ ENTRY(iret_exc)
.previous
_ASM_EXTABLE(irq_return,iret_exc)
+#ifdef CONFIG_X86_ESPFIX32
CFI_RESTORE_STATE
ldt_ss:
#ifdef CONFIG_PARAVIRT
@@ -594,6 +597,7 @@ ldt_ss:
lss (%esp), %esp /* switch to espfix segment */
CFI_ADJUST_CFA_OFFSET -8
jmp restore_nocheck
+#endif
CFI_ENDPROC
ENDPROC(system_call)
@@ -706,6 +710,7 @@ END(syscall_badsys)
* the high word of the segment base from the GDT and swiches to the
* normal stack and adjusts ESP with the matching offset.
*/
+#ifdef CONFIG_X86_ESPFIX32
/* fixup the stack */
mov GDT_ESPFIX_SS + 4, %al /* bits 16..23 */
mov GDT_ESPFIX_SS + 7, %ah /* bits 24..31 */
@@ -715,8 +720,10 @@ END(syscall_badsys)
pushl_cfi %eax
lss (%esp), %esp /* switch to the normal stack segment */
CFI_ADJUST_CFA_OFFSET -8
+#endif
.endm
.macro UNWIND_ESPFIX_STACK
+#ifdef CONFIG_X86_ESPFIX32
movl %ss, %eax
/* see if on espfix stack */
cmpw $__ESPFIX_SS, %ax
@@ -727,6 +734,7 @@ END(syscall_badsys)
/* switch to normal stack */
FIXUP_ESPFIX_STACK
27:
+#endif
.endm
/*
@@ -1357,11 +1365,13 @@ END(debug)
ENTRY(nmi)
RING0_INT_FRAME
ASM_CLAC
+#ifdef CONFIG_X86_ESPFIX32
pushl_cfi %eax
movl %ss, %eax
cmpw $__ESPFIX_SS, %ax
popl_cfi %eax
je nmi_espfix_stack
+#endif
cmpl $ia32_sysenter_target,(%esp)
je nmi_stack_fixup
pushl_cfi %eax
@@ -1401,6 +1411,7 @@ nmi_debug_stack_check:
FIX_STACK 24, nmi_stack_correct, 1
jmp nmi_stack_correct
+#ifdef CONFIG_X86_ESPFIX32
nmi_espfix_stack:
/* We have a RING0_INT_FRAME here.
*
@@ -1422,6 +1433,7 @@ nmi_espfix_stack:
lss 12+4(%esp), %esp # back to espfix stack
CFI_ADJUST_CFA_OFFSET -24
jmp irq_return
+#endif
CFI_ENDPROC
END(nmi)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index bffaa98..da0b9bd 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1045,8 +1045,10 @@ irq_return:
* Are we returning to a stack segment from the LDT? Note: in
* 64-bit mode SS:RSP on the exception stack is always valid.
*/
+#ifdef CONFIG_X86_ESPFIX64
testb $4,(SS-RIP)(%rsp)
jnz irq_return_ldt
+#endif
irq_return_iret:
INTERRUPT_RETURN
@@ -1058,6 +1060,7 @@ ENTRY(native_iret)
_ASM_EXTABLE(native_iret, bad_iret)
#endif
+#ifdef CONFIG_X86_ESPFIX64
irq_return_ldt:
pushq_cfi %rax
pushq_cfi %rdi
@@ -1081,6 +1084,7 @@ irq_return_ldt:
movq %rax,%rsp
popq_cfi %rax
jmp irq_return_iret
+#endif
.section .fixup,"ax"
bad_iret:
@@ -1152,6 +1156,7 @@ END(common_interrupt)
* modify the stack to make it look like we just entered
* the #GP handler from user space, similar to bad_iret.
*/
+#ifdef CONFIG_X86_ESPFIX64
ALIGN
__do_double_fault:
XCPT_FRAME 1 RDI+8
@@ -1177,6 +1182,9 @@ __do_double_fault:
retq
CFI_ENDPROC
END(__do_double_fault)
+#else
+# define __do_double_fault do_double_fault
+#endif
/*
* End of kprobes section
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index ebc9873..c37886d 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -229,6 +229,11 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
}
}
+ if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
+ error = -EINVAL;
+ goto out_unlock;
+ }
+
fill_ldt(&ldt, &ldt_info);
if (oldmode)
ldt.avl = 0;
--
1.9.1
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