linux-kernel - [PATCH v2 1/6] kexec_file: Add buffer hand-over support for the next kernel

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Message-Id: <1471058305-30198-2-git-send-email-bauerman@linux.vnet.ibm.com>
Date:	Sat, 13 Aug 2016 00:18:20 -0300
From:	Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
To:	kexec@...ts.infradead.org
Cc:	linux-security-module@...r.kernel.org,
	linux-ima-devel@...ts.sourceforge.net,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, Eric Biederman <ebiederm@...ssion.com>,
	Dave Young <dyoung@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, Baoquan He <bhe@...hat.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Stewart Smith <stewart@...ux.vnet.ibm.com>,
	Samuel Mendoza-Jonas <sam@...dozajonas.com>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Eric Richter <erichte@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Petko Manolov <petkan@...-labs.com>,
	David Laight <David.Laight@...LAB.COM>,
	Balbir Singh <bsingharora@...il.com>,
	Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
Subject: [PATCH v2 1/6] kexec_file: Add buffer hand-over support for the next kernel

The buffer hand-over mechanism allows the currently running kernel to pass
data to kernel that will be kexec'd via a kexec segment. The second kernel
can check whether the previous kernel sent data and retrieve it.

This is the architecture-independent part of the feature.

Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
---
 include/linux/kexec.h | 29 ++++++++++++++++++++++
 kernel/kexec_file.c   | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index ceccc5856aab..4559a1a01b0a 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -388,6 +388,35 @@ static inline void *boot_phys_to_virt(unsigned long entry)
 	return phys_to_virt(boot_phys_to_phys(entry));
 }
 
+#ifdef CONFIG_KEXEC_FILE
+bool __weak kexec_can_hand_over_buffer(void);
+int __weak arch_kexec_add_handover_buffer(struct kimage *image,
+					  unsigned long load_addr,
+					  unsigned long size);
+int kexec_add_handover_buffer(struct kexec_buf *kbuf);
+int __weak kexec_get_handover_buffer(void **addr, unsigned long *size);
+int __weak kexec_free_handover_buffer(void);
+#else
+static inline bool kexec_can_hand_over_buffer(void)
+{
+	return false;
+}
+
+static inline int kexec_add_handover_buffer(struct kexec_buf *kbuf)
+{
+	return -ENOTSUPP;
+}
+
+static inline int kexec_get_handover_buffer(void **addr, unsigned long *size)
+{
+	return -ENOTSUPP;
+}
+
+static inline int kexec_free_handover_buffer(void)
+{
+	return -ENOTSUPP;
+}
+#endif /* CONFIG_KEXEC_FILE */
 #else /* !CONFIG_KEXEC_CORE */
 struct pt_regs;
 struct task_struct;
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 772cb491715e..c8418d62e2fc 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -135,6 +135,74 @@ int __weak arch_kexec_verify_buffer(enum kexec_file_type type, const void *buf,
 	return -EINVAL;
 }
 
+/**
+ * kexec_can_hand_over_buffer - can we pass data to the kexec'd kernel?
+ */
+bool __weak kexec_can_hand_over_buffer(void)
+{
+	return false;
+}
+
+/**
+ * arch_kexec_add_handover_buffer - do arch-specific steps to handover buffer
+ *
+ * Architectures should use this function to pass on the handover buffer
+ * information to the next kernel.
+ *
+ * Return: 0 on success, negative errno on error.
+ */
+int __weak arch_kexec_add_handover_buffer(struct kimage *image,
+					  unsigned long load_addr,
+					  unsigned long size)
+{
+	return -ENOTSUPP;
+}
+
+/**
+ * kexec_add_handover_buffer - add buffer to be used by the next kernel
+ * @kbuf:	Buffer contents and memory parameters.
+ *
+ * This function assumes that kexec_mutex is held.
+ * On successful return, @kbuf->mem will have the physical address of
+ * the buffer in the next kernel.
+ *
+ * Return: 0 on success, negative errno on error.
+ */
+int kexec_add_handover_buffer(struct kexec_buf *kbuf)
+{
+	int ret;
+
+	if (!kexec_can_hand_over_buffer())
+		return -ENOTSUPP;
+
+	ret = kexec_add_buffer(kbuf);
+	if (ret)
+		return ret;
+
+	return arch_kexec_add_handover_buffer(kbuf->image, kbuf->mem,
+					      kbuf->memsz);
+}
+
+/**
+ * kexec_get_handover_buffer - get the handover buffer from the previous kernel
+ * @addr:	On successful return, set to point to the buffer contents.
+ * @size:	On successful return, set to the buffer size.
+ *
+ * Return: 0 on success, negative errno on error.
+ */
+int __weak kexec_get_handover_buffer(void **addr, unsigned long *size)
+{
+	return -ENOTSUPP;
+}
+
+/**
+ * kexec_free_handover_buffer - free memory used by the handover buffer
+ */
+int __weak kexec_free_handover_buffer(void)
+{
+	return -ENOTSUPP;
+}
+
 /*
  * In file mode list of segments is prepared by kernel. Copy relevant
  * data from user space, do error checking, prepare segment list
-- 
1.9.1