[tip: x86/sgx] x86/cpu/intel: Add a nosgx kernel parameter

[tip-bot2 for Jarkko Sakkinen]

The following commit has been merged into the x86/sgx branch of tip:

Commit-ID:     38853a303982e3be3eccb1a1132399a5c5e2d806
Gitweb:        https://git.kernel.org/tip/38853a303982e3be3eccb1a1132399a5c5e2d806
Author:        Jarkko Sakkinen <jarkko@xxxxxxxxxx>
AuthorDate:    Fri, 13 Nov 2020 00:01:19 +02:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 17 Nov 2020 14:36:13 +01:00

x86/cpu/intel: Add a nosgx kernel parameter

Add a kernel parameter to disable SGX kernel support and document it.

 [ bp: Massage. ]

Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Acked-by: Jethro Beekman <jethro@xxxxxxxxxxxx>
Tested-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20201112220135.165028-9-jarkko@xxxxxxxxxx
---
 Documentation/admin-guide/kernel-parameters.txt |  2 ++
 arch/x86/kernel/cpu/feat_ctl.c                  |  9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 526d65d..42d1528 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3368,6 +3368,8 @@
 
 	nosep		[BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
 
+	nosgx		[X86-64,SGX] Disables Intel SGX kernel support.
+
 	nosmp		[SMP] Tells an SMP kernel to act as a UP kernel,
 			and disable the IO APIC.  legacy for "maxcpus=0".
 
diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c
index d38e973..3b1b01f 100644
--- a/arch/x86/kernel/cpu/feat_ctl.c
+++ b/arch/x86/kernel/cpu/feat_ctl.c
@@ -99,6 +99,15 @@ static void clear_sgx_caps(void)
 	setup_clear_cpu_cap(X86_FEATURE_SGX_LC);
 }
 
+static int __init nosgx(char *str)
+{
+	clear_sgx_caps();
+
+	return 0;
+}
+
+early_param("nosgx", nosgx);
+
 void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
 {
 	bool tboot = tboot_enabled();