linux-kernel - [tip: x86/urgent] x86/cpu: Fix check for RDPKRU in __show

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Date: Wed, 24 Apr 2024 12:43:15 -0000
From: "tip-bot2 for David Kaplan" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: David Kaplan <david.kaplan@....com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/cpu: Fix check for RDPKRU in __show_regs()

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

Commit-ID:     b53c6bd5d271d023857174b8fd3e32f98ae51372
Gitweb:        https://git.kernel.org/tip/b53c6bd5d271d023857174b8fd3e32f98ae51372
Author:        David Kaplan <david.kaplan@....com>
AuthorDate:    Sun, 21 Apr 2024 21:17:28 +02:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Wed, 24 Apr 2024 14:30:21 +02:00

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@....com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Link: https://lore.kernel.org/r/20240421191728.32239-1-bp@kernel.org
---
 arch/x86/kernel/process_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 7062b84..6d3d20e 100644
--- 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());
 }