linux-kernel - [tip: x86/shstk] x86/shstk: Add ARCH_SHSTK

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Message-ID: <168694301105.404.1532533870683131985.tip-bot2@tip-bot2>
Date:   Fri, 16 Jun 2023 19:16:51 -0000
From:   "tip-bot2 for Mike Rapoport" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Mike Rapoport <rppt@...ux.ibm.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Borislav Petkov (AMD)" <bp@...en8.de>,
        Kees Cook <keescook@...omium.org>,
        David Hildenbrand <david@...hat.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        John Allen <john.allen@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/shstk] x86/shstk: Add ARCH_SHSTK_UNLOCK

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

Commit-ID:     7a95f0591bbf36f26059ae02b8d341e77333e00c
Gitweb:        https://git.kernel.org/tip/7a95f0591bbf36f26059ae02b8d341e77333e00c
Author:        Mike Rapoport <rppt@...ux.ibm.com>
AuthorDate:    Mon, 12 Jun 2023 17:11:07 -07:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Thu, 15 Jun 2023 16:31:35 -07:00

x86/shstk: Add ARCH_SHSTK_UNLOCK

Userspace loaders may lock features before a CRIU restore operation has
the chance to set them to whatever state is required by the process
being restored. Allow a way for CRIU to unlock features. Add it as an
arch_prctl() like the other shadow stack operations, but restrict it being
called by the ptrace arch_pctl() interface.

[Merged into recent API changes, added commit log and docs]

Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Kees Cook <keescook@...omium.org>
Reviewed-by: David Hildenbrand <david@...hat.com>
Tested-by: Pengfei Xu <pengfei.xu@...el.com>
Tested-by: John Allen <john.allen@....com>
Tested-by: Kees Cook <keescook@...omium.org>
Link: https://lore.kernel.org/all/20230613001108.3040476-42-rick.p.edgecombe%40intel.com
---
 Documentation/arch/x86/shstk.rst  |  4 ++++
 arch/x86/include/uapi/asm/prctl.h |  1 +
 arch/x86/kernel/process_64.c      |  1 +
 arch/x86/kernel/shstk.c           |  9 +++++++--
 4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/Documentation/arch/x86/shstk.rst b/Documentation/arch/x86/shstk.rst
index f09afa5..f3553cc 100644
--- a/Documentation/arch/x86/shstk.rst
+++ b/Documentation/arch/x86/shstk.rst
@@ -75,6 +75,10 @@ arch_prctl(ARCH_SHSTK_LOCK, unsigned long features)
     are ignored. The mask is ORed with the existing value. So any feature bits
     set here cannot be enabled or disabled afterwards.
 
+arch_prctl(ARCH_SHSTK_UNLOCK, unsigned long features)
+    Unlock features. 'features' is a mask of all features to unlock. All
+    bits set are processed, unset bits are ignored. Only works via ptrace.
+
 The return values are as follows. On success, return 0. On error, errno can
 be::
 
diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
index eedfde3..3189c4a 100644
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -33,6 +33,7 @@
 #define ARCH_SHSTK_ENABLE		0x5001
 #define ARCH_SHSTK_DISABLE		0x5002
 #define ARCH_SHSTK_LOCK			0x5003
+#define ARCH_SHSTK_UNLOCK		0x5004
 
 /* ARCH_SHSTK_ features bits */
 #define ARCH_SHSTK_SHSTK		(1ULL <<  0)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 0f89aa0..e6db21c 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -899,6 +899,7 @@ long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
 	case ARCH_SHSTK_ENABLE:
 	case ARCH_SHSTK_DISABLE:
 	case ARCH_SHSTK_LOCK:
+	case ARCH_SHSTK_UNLOCK:
 		return shstk_prctl(task, option, arg2);
 	default:
 		ret = -EINVAL;
diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index d723cdc..d43b7a9 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -489,9 +489,14 @@ long shstk_prctl(struct task_struct *task, int option, unsigned long features)
 		return 0;
 	}
 
-	/* Don't allow via ptrace */
-	if (task != current)
+	/* Only allow via ptrace */
+	if (task != current) {
+		if (option == ARCH_SHSTK_UNLOCK && IS_ENABLED(CONFIG_CHECKPOINT_RESTORE)) {
+			task->thread.features_locked &= ~features;
+			return 0;
+		}
 		return -EINVAL;
+	}
 
 	/* Do not allow to change locked features */
 	if (features & task->thread.features_locked)