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x86/cpu: Remove CONFIG_X86_SMAP and "nosmap"

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Those were added as part of the SMAP enablement but SMAP is currently
an integral part of kernel proper and there's no need to disable it
anymore.

Rip out that functionality. Leave --uaccess default on for objtool as
this is what objtool should do by default anyway.

If still needed - clearcpuid=smap.

Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220127115626.14179-4-bp@alien8.de
This commit is contained in:
Borislav Petkov 2022-01-27 12:56:23 +01:00
parent c949110ef4
commit dbae0a934f
9 changed files with 10 additions and 71 deletions
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2
Documentation/admin-guide/kernel-parameters.txt
View File

@ -3461,7 +3461,7 @@
noexec=on: enable non-executable mappings (default)
noexec=off: disable non-executable mappings
nosmap [X86,PPC]
nosmap [PPC]
Disable SMAP (Supervisor Mode Access Prevention)
even if it is supported by processor.

5
Documentation/x86/cpuinfo.rst
View File

@ -140,9 +140,8 @@ from #define X86_FEATURE_UMIP (16*32 + 2).
In addition, there exists a variety of custom command-line parameters that
disable specific features. The list of parameters includes, but is not limited
to, nofsgsbase, nosmap, and nosmep. 5-level paging can also be disabled using
"no5lvl". SMAP and SMEP are disabled with the aforementioned parameters,
respectively.
to, nofsgsbase, and nosmep. 5-level paging can also be disabled using
"no5lvl". SMEP is disabled with the aforementioned parameter.
e: The feature was known to be non-functional.
----------------------------------------------

11
arch/x86/Kconfig
View File

@ -1816,17 +1816,6 @@ config ARCH_RANDOM
If supported, this is a high bandwidth, cryptographically
secure hardware random number generator.
config X86_SMAP
def_bool y
prompt "Supervisor Mode Access Prevention" if EXPERT
help
Supervisor Mode Access Prevention (SMAP) is a security
feature in newer Intel processors. There is a small
performance cost if this enabled and turned on; there is
also a small increase in the kernel size if this is enabled.
If unsure, say Y.
config X86_UMIP
def_bool y
prompt "User Mode Instruction Prevention" if EXPERT

8
arch/x86/include/asm/disabled-features.h
View File

@ -10,12 +10,6 @@
* cpu_feature_enabled().
*/
#ifdef CONFIG_X86_SMAP
# define DISABLE_SMAP 0
#else
# define DISABLE_SMAP (1<<(X86_FEATURE_SMAP & 31))
#endif
#ifdef CONFIG_X86_UMIP
# define DISABLE_UMIP 0
#else
@ -80,7 +74,7 @@
#define DISABLED_MASK6 0
#define DISABLED_MASK7 (DISABLE_PTI)
#define DISABLED_MASK8 0
#define DISABLED_MASK9 (DISABLE_SMAP|DISABLE_SGX)
#define DISABLED_MASK9 (DISABLE_SGX)
#define DISABLED_MASK10 0
#define DISABLED_MASK11 0
#define DISABLED_MASK12 0

24
arch/x86/include/asm/smap.h
View File

@ -19,25 +19,14 @@
#ifdef __ASSEMBLY__
#ifdef CONFIG_X86_SMAP
#define ASM_CLAC \
ALTERNATIVE "", __ASM_CLAC, X86_FEATURE_SMAP
#define ASM_STAC \
ALTERNATIVE "", __ASM_STAC, X86_FEATURE_SMAP
#else /* CONFIG_X86_SMAP */
#define ASM_CLAC
#define ASM_STAC
#endif /* CONFIG_X86_SMAP */
#else /* __ASSEMBLY__ */
#ifdef CONFIG_X86_SMAP
static __always_inline void clac(void)
{
/* Note: a barrier is implicit in alternative() */
@ -76,19 +65,6 @@ static __always_inline void smap_restore(unsigned long flags)
#define ASM_STAC \
ALTERNATIVE("", __ASM_STAC, X86_FEATURE_SMAP)
#else /* CONFIG_X86_SMAP */
static inline void clac(void) { }
static inline void stac(void) { }
static inline unsigned long smap_save(void) { return 0; }
static inline void smap_restore(unsigned long flags) { }
#define ASM_CLAC
#define ASM_STAC
#endif /* CONFIG_X86_SMAP */
#endif /* __ASSEMBLY__ */
#endif /* _ASM_X86_SMAP_H */

15
arch/x86/kernel/cpu/common.c
View File

@ -382,13 +382,6 @@ static __always_inline void setup_smep(struct cpuinfo_x86 *c)
cr4_set_bits(X86_CR4_SMEP);
}
static __init int setup_disable_smap(char *arg)
{
setup_clear_cpu_cap(X86_FEATURE_SMAP);
return 1;
}
__setup("nosmap", setup_disable_smap);
static __always_inline void setup_smap(struct cpuinfo_x86 *c)
{
unsigned long eflags = native_save_fl();
@ -396,14 +389,8 @@ static __always_inline void setup_smap(struct cpuinfo_x86 *c)
/* This should have been cleared long ago */
BUG_ON(eflags & X86_EFLAGS_AC);
if (cpu_has(c, X86_FEATURE_SMAP)) {
#ifdef CONFIG_X86_SMAP
if (cpu_has(c, X86_FEATURE_SMAP))
cr4_set_bits(X86_CR4_SMAP);
#else
clear_cpu_cap(c, X86_FEATURE_SMAP);
cr4_clear_bits(X86_CR4_SMAP);
#endif
}
}
static __always_inline void setup_umip(struct cpuinfo_x86 *c)

2
scripts/Makefile.build
View File

@ -233,7 +233,7 @@ objtool_args = \
$(if $(CONFIG_FRAME_POINTER),, --no-fp) \
$(if $(CONFIG_GCOV_KERNEL)$(CONFIG_LTO_CLANG), --no-unreachable)\
$(if $(CONFIG_RETPOLINE), --retpoline) \
$(if $(CONFIG_X86_SMAP), --uaccess) \
--uaccess \
$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount) \
$(if $(CONFIG_SLS), --sls)

6
scripts/link-vmlinux.sh
View File

@ -146,9 +146,9 @@ objtool_link()
if is_enabled CONFIG_RETPOLINE; then
objtoolopt="${objtoolopt} --retpoline"
fi
if is_enabled CONFIG_X86_SMAP; then
objtoolopt="${objtoolopt} --uaccess"
fi
objtoolopt="${objtoolopt} --uaccess"
if is_enabled CONFIG_SLS; then
objtoolopt="${objtoolopt} --sls"
fi

8
tools/arch/x86/include/asm/disabled-features.h
View File

@ -10,12 +10,6 @@
* cpu_feature_enabled().
*/
#ifdef CONFIG_X86_SMAP
# define DISABLE_SMAP 0
#else
# define DISABLE_SMAP (1<<(X86_FEATURE_SMAP & 31))
#endif
#ifdef CONFIG_X86_UMIP
# define DISABLE_UMIP 0
#else
@ -80,7 +74,7 @@
#define DISABLED_MASK6 0
#define DISABLED_MASK7 (DISABLE_PTI)
#define DISABLED_MASK8 0
#define DISABLED_MASK9 (DISABLE_SMAP|DISABLE_SGX)
#define DISABLED_MASK9 (DISABLE_SGX)
#define DISABLED_MASK10 0
#define DISABLED_MASK11 0
#define DISABLED_MASK12 0