x86/cpu: Fix check for RDPKRU in __show_regs()

cpu_feature_enabled(X86_FEATURE_OSPKE) does not necessarily reflect
whether CR4.PKE is set on the CPU.  In particular, they may differ on
non-BSP CPUs before setup_pku() is executed.  In this scenario, RDPKRU
will #UD causing the system to hang.

Fix by checking CR4 for PKE enablement which is always correct for the
current CPU.

The scenario happens by inserting a WARN* before setup_pku() in
identiy_cpu() or some other diagnostic which would lead to calling
__show_regs().

  [ bp: Massage commit message. ]

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240421191728.32239-1-bp@kernel.org

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 7062b84dd467d62ac1aed8c4fe4bdb86d5a7ac61..6d3d20e3e43a9b005f725d1e89dcc8fd81560dcd 100644 (file)
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -139,7 +139,7 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode mode,
                       log_lvl, d3, d6, d7);
        }
 
-       if (cpu_feature_enabled(X86_FEATURE_OSPKE))
+       if (cr4 & X86_CR4_PKE)
                printk("%sPKRU: %08x\n", log_lvl, read_pkru());
 }