[PATCHv6 15/16] x86/cpu: Enable LASS during CPU initialization

Kirill A. Shutemov
2025-06-20T13:53:54Z

From: Sohil Mehta <sohil.mehta@intel.com>

Being a security feature, enable LASS by default if the platform
supports it.

While at it, get rid of the comment above the SMAP/SMEP/UMIP/LASS setup
instead of updating it to mention LASS as well, as the whole sequence is
quite self-explanatory.

Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/kernel/cpu/common.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d12ce36a76f5..edb342214328 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -401,6 +401,12 @@ static __always_inline void setup_umip(struct cpuinfo_x86 *c)
cr4_clear_bits(X86_CR4_UMIP);
}

+static __always_inline void setup_lass(struct cpuinfo_x86 *c)
+{
+ if (cpu_feature_enabled(X86_FEATURE_LASS))
+ cr4_set_bits(X86_CR4_LASS);
+}
+
/* These bits should not change their value after CPU init is finished. */
static const unsigned long cr4_pinned_mask = X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP |
X86_CR4_FSGSBASE | X86_CR4_CET | X86_CR4_FRED |
@@ -1975,10 +1981,10 @@ static void identify_cpu(struct cpuinfo_x86 *c)
/* Disable the PN if appropriate */
squash_the_stupid_serial_number(c);

- /* Set up SMEP/SMAP/UMIP */
setup_smep(c);
setup_smap(c);
setup_umip(c);
+ setup_lass(c);

/* Enable FSGSBASE instructions if available. */
if (cpu_has(c, X86_FEATURE_FSGSBASE)) {
--
2.47.2