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x86/math-emu: Limit MATH_EMULATION to 486SX compatibles 

The FPU emulation code is old and fragile in places, try to limit its
use to builds for CPUs that actually use it. As far as I can tell,
this is only true for i486sx compatibles, including the Cyrix 486SLC,
AMD Am486SX and ÉLAN SC410, UMC U5S amd DM&P VortexSX86, all of which
were relatively short-lived and got replaced with i486DX compatible
processors soon after introduction, though some of the embedded versions
remained available much longer.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Bill Metzenthen <billm@melbpc.org.au>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20191001142344.1274185-2-arnd@arndb.de
This commit is contained in:
Arnd Bergmann 2019-10-01 16:23:35 +02:00 committed by Borislav Petkov
parent e6b44ce192
commit 87d6021b81
4 changed files with 20 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/Kconfig
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@ -1751,7 +1751,7 @@ config X86_RESERVE_LOW
config MATH_EMULATION
bool
depends on MODIFY_LDT_SYSCALL
prompt "Math emulation" if X86_32
prompt "Math emulation" if X86_32 && (M486SX || MELAN)
---help---
Linux can emulate a math coprocessor (used for floating point
operations) if you don't have one. 486DX and Pentium processors have

25
arch/x86/Kconfig.cpu
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@ -50,12 +50,19 @@ choice
See each option's help text for additional details. If you don't know
what to do, choose "486".
config M486SX
bool "486SX"
depends on X86_32
---help---
Select this for an 486-class CPU without an FPU such as
AMD/Cyrix/IBM/Intel SL/SLC/SLC2/SLC3/SX/SX2 and UMC U5S.
config M486
bool "486"
bool "486DX"
depends on X86_32
---help---
Select this for an 486-class CPU such as AMD/Cyrix/IBM/Intel
486DX/DX2/DX4 or SL/SLC/SLC2/SLC3/SX/SX2 and UMC U5D or U5S.
486DX/DX2/DX4 and UMC U5D.
config M586
bool "586/K5/5x86/6x86/6x86MX"
@ -312,20 +319,20 @@ config X86_L1_CACHE_SHIFT
int
default "7" if MPENTIUM4 || MPSC
default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU
default "4" if MELAN || M486 || MGEODEGX1
default "4" if MELAN || M486SX || M486 || MGEODEGX1
default "5" if MWINCHIP3D || MWINCHIPC6 || MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODE_LX
config X86_F00F_BUG
def_bool y
depends on M586MMX || M586TSC || M586 || M486
depends on M586MMX || M586TSC || M586 || M486SX || M486
config X86_INVD_BUG
def_bool y
depends on M486
depends on M486SX || M486
config X86_ALIGNMENT_16
def_bool y
depends on MWINCHIP3D || MWINCHIPC6 || MCYRIXIII || MELAN || MK6 || M586MMX || M586TSC || M586 || M486 || MVIAC3_2 || MGEODEGX1
depends on MWINCHIP3D || MWINCHIPC6 || MCYRIXIII || MELAN || MK6 || M586MMX || M586TSC || M586 || M486SX || M486 || MVIAC3_2 || MGEODEGX1
config X86_INTEL_USERCOPY
def_bool y
@ -378,7 +385,7 @@ config X86_MINIMUM_CPU_FAMILY
config X86_DEBUGCTLMSR
def_bool y
depends on !(MK6 || MWINCHIPC6 || MWINCHIP3D || MCYRIXIII || M586MMX || M586TSC || M586 || M486) && !UML
depends on !(MK6 || MWINCHIPC6 || MWINCHIP3D || MCYRIXIII || M586MMX || M586TSC || M586 || M486SX || M486) && !UML
menuconfig PROCESSOR_SELECT
bool "Supported processor vendors" if EXPERT
@ -402,7 +409,7 @@ config CPU_SUP_INTEL
config CPU_SUP_CYRIX_32
default y
bool "Support Cyrix processors" if PROCESSOR_SELECT
depends on M486 || M586 || M586TSC || M586MMX || (EXPERT && !64BIT)
depends on M486SX || M486 || M586 || M586TSC || M586MMX || (EXPERT && !64BIT)
---help---
This enables detection, tunings and quirks for Cyrix processors
@ -470,7 +477,7 @@ config CPU_SUP_TRANSMETA_32
config CPU_SUP_UMC_32
default y
bool "Support UMC processors" if PROCESSOR_SELECT
depends on M486 || (EXPERT && !64BIT)
depends on M486SX || M486 || (EXPERT && !64BIT)
---help---
This enables detection, tunings and quirks for UMC processors

1
arch/x86/Makefile_32.cpu
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@ -10,6 +10,7 @@ else
tune = $(call cc-option,-mcpu=$(1),$(2))
endif
cflags-$(CONFIG_M486SX) += -march=i486
cflags-$(CONFIG_M486) += -march=i486
cflags-$(CONFIG_M586) += -march=i586
cflags-$(CONFIG_M586TSC) += -march=i586

2
arch/x86/include/asm/module.h
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@ -15,6 +15,8 @@ struct mod_arch_specific {
#ifdef CONFIG_X86_64
/* X86_64 does not define MODULE_PROC_FAMILY */
#elif defined CONFIG_M486SX
#define MODULE_PROC_FAMILY "486SX "
#elif defined CONFIG_M486
#define MODULE_PROC_FAMILY "486 "
#elif defined CONFIG_M586