linux-kernel - [tip: x86/urgent] x86/kexec: Fix bug with call depth tracking

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Date: Wed, 05 Jun 2024 08:05:05 -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>,
 Tom Lendacky <thomas.lendacky@....com>,  <stable@...nel.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/kexec: Fix bug with call depth tracking

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

Commit-ID:     93c1800b3799f17375989b0daf76497dd3e80922
Gitweb:        https://git.kernel.org/tip/93c1800b3799f17375989b0daf76497dd3e80922
Author:        David Kaplan <david.kaplan@....com>
AuthorDate:    Sun, 02 Jun 2024 13:19:09 -05:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Mon, 03 Jun 2024 17:19:03 +02:00

x86/kexec: Fix bug with call depth tracking

The call to cc_platform_has() triggers a fault and system crash if call depth
tracking is active because the GS segment has been reset by load_segments() and
GS_BASE is now 0 but call depth tracking uses per-CPU variables to operate.

Call cc_platform_has() earlier in the function when GS is still valid.

  [ bp: Massage. ]

Fixes: 5d8213864ade ("x86/retbleed: Add SKL return thunk")
Signed-off-by: David Kaplan <david.kaplan@....com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
Cc: <stable@...nel.org>
Link: https://lore.kernel.org/r/20240603083036.637-1-bp@kernel.org
---
 arch/x86/kernel/machine_kexec_64.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index b180d8e..cc0f7f7 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -295,8 +295,15 @@ void machine_kexec_cleanup(struct kimage *image)
 void machine_kexec(struct kimage *image)
 {
 	unsigned long page_list[PAGES_NR];
-	void *control_page;
+	unsigned int host_mem_enc_active;
 	int save_ftrace_enabled;
+	void *control_page;
+
+	/*
+	 * This must be done before load_segments() since if call depth tracking
+	 * is used then GS must be valid to make any function calls.
+	 */
+	host_mem_enc_active = cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT);
 
 #ifdef CONFIG_KEXEC_JUMP
 	if (image->preserve_context)
@@ -358,7 +365,7 @@ void machine_kexec(struct kimage *image)
 				       (unsigned long)page_list,
 				       image->start,
 				       image->preserve_context,
-				       cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT));
+				       host_mem_enc_active);
 
 #ifdef CONFIG_KEXEC_JUMP
 	if (image->preserve_context)