[PATCH v2 0/2] powerpc: Add PowerPC Capabilities ELF note

[PATCH v2 0/2] powerpc: Add PowerPC Capabilities ELF note

[Maxiwell S. Garcia]

The first patch adds the PowerPC name and the PPC_ELFNOTE_CAPABILITIES
type in the kernel binary ELF note. This type is a bitmap that can be
used to advertise kernel capabilities to userland.

The second patch adds a new documentation file to detail the
ELF Note PowerPC namespace and the PPC_ELFNOTE_CAPABILITIES type.

V2:
* Create the header arch/powerpc/include/asm/elfnote.h with the
  new type PPC_ELFNOTE_CAPABILITIES
* Add documentation file in powerpc dir

Claudio Carvalho (1):
  powerpc: Add PowerPC Capabilities ELF note

Maxiwell S. Garcia (1):
  docs: powerpc: Add ELF note documentation

 Documentation/powerpc/elfnote.rst  | 42 ++++++++++++++++++++++++++++++
 arch/powerpc/include/asm/elfnote.h | 24 +++++++++++++++++
 arch/powerpc/kernel/Makefile       |  2 +-
 arch/powerpc/kernel/note.S         | 40 ++++++++++++++++++++++++++++
 4 files changed, 107 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/powerpc/elfnote.rst
 create mode 100644 arch/powerpc/include/asm/elfnote.h
 create mode 100644 arch/powerpc/kernel/note.S

-- 
2.20.1

[PATCH v2 1/2] powerpc: Add PowerPC Capabilities ELF note

[Maxiwell S. Garcia]

From: Claudio Carvalho <cclaudio@linux.ibm.com>

Add the PowerPC name and the PPC_ELFNOTE_CAPABILITIES type in the
kernel binary ELF note. This type is a bitmap that can be used to
advertise kernel capabilities to userland.

This patch also defines PPCCAP_ULTRAVISOR_BIT as being the bit zero.

Suggested-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
[ maxiwell: Define the 'PowerPC' type in the elfnote.h ]
Signed-off-by: Maxiwell S. Garcia <maxiwell@linux.ibm.com>
---
 arch/powerpc/include/asm/elfnote.h | 24 ++++++++++++++++++
 arch/powerpc/kernel/Makefile       |  2 +-
 arch/powerpc/kernel/note.S         | 40 ++++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+), 1 deletion(-)
 create mode 100644 arch/powerpc/include/asm/elfnote.h
 create mode 100644 arch/powerpc/kernel/note.S

diff --git a/arch/powerpc/include/asm/elfnote.h b/arch/powerpc/include/asm/elfnote.h
new file mode 100644
index 000000000000..a201b6e9ae44
--- /dev/null
+++ b/arch/powerpc/include/asm/elfnote.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * PowerPC ELF notes.
+ *
+ * Copyright 2019, IBM Corporation
+ */
+
+#ifndef __ASM_POWERPC_ELFNOTE_H__
+#define __ASM_POWERPC_ELFNOTE_H__
+
+/*
+ * These note types should live in a SHT_NOTE segment and have
+ * "PowerPC" in the name field.
+ */
+
+/*
+ * The capabilities supported/required by this kernel (bitmap).
+ *
+ * This type uses a bitmap as "desc" field. Each bit is described
+ * in arch/powerpc/kernel/note.S
+ */
+#define PPC_ELFNOTE_CAPABILITIES 1
+
+#endif /* __ASM_POWERPC_ELFNOTE_H__ */
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 56dfa7a2a6f2..0fcd3045284f 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -52,7 +52,7 @@ obj-y				:= cputable.o ptrace.o syscalls.o \
 				   of_platform.o prom_parse.o
 obj-$(CONFIG_PPC64)		+= setup_64.o sys_ppc32.o \
 				   signal_64.o ptrace32.o \
-				   paca.o nvram_64.o firmware.o
+				   paca.o nvram_64.o firmware.o note.o
 obj-$(CONFIG_VDSO32)		+= vdso32/
 obj-$(CONFIG_PPC_WATCHDOG)	+= watchdog.o
 obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
diff --git a/arch/powerpc/kernel/note.S b/arch/powerpc/kernel/note.S
new file mode 100644
index 000000000000..bcdad15395dd
--- /dev/null
+++ b/arch/powerpc/kernel/note.S
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * PowerPC ELF notes.
+ *
+ * Copyright 2019, IBM Corporation
+ */
+
+#include <linux/elfnote.h>
+#include <asm/elfnote.h>
+
+/*
+ * Ultravisor-capable bit (PowerNV only).
+ *
+ * Bit 0 indicates that the powerpc kernel binary knows how to run in an
+ * ultravisor-enabled system.
+ *
+ * In an ultravisor-enabled system, some machine resources are now controlled
+ * by the ultravisor. If the kernel is not ultravisor-capable, but it ends up
+ * being run on a machine with ultravisor, the kernel will probably crash
+ * trying to access ultravisor resources. For instance, it may crash in early
+ * boot trying to set the partition table entry 0.
+ *
+ * In an ultravisor-enabled system, a bootloader could warn the user or prevent
+ * the kernel from being run if the PowerPC ultravisor capability doesn't exist
+ * or the Ultravisor-capable bit is not set.
+ */
+#ifdef CONFIG_PPC_POWERNV
+#define PPCCAP_ULTRAVISOR_BIT		(1 << 0)
+#else
+#define PPCCAP_ULTRAVISOR_BIT		0
+#endif
+
+/*
+ * Add the PowerPC Capabilities in the binary ELF note. It is a bitmap that
+ * can be used to advertise kernel capabilities to userland.
+ */
+#define PPC_CAPABILITIES_BITMAP (PPCCAP_ULTRAVISOR_BIT)
+
+ELFNOTE(PowerPC, PPC_ELFNOTE_CAPABILITIES,
+	.long PPC_CAPABILITIES_BITMAP)
-- 
2.20.1

[PATCH v2 2/2] docs: powerpc: Add ELF note documentation

[Maxiwell S. Garcia]

The ELF note documentation describes the types and descriptors to be
used with the PowerPC namespace.

Signed-off-by: Maxiwell S. Garcia <maxiwell@linux.ibm.com>
Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
---
 Documentation/powerpc/elfnote.rst | 42 +++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 Documentation/powerpc/elfnote.rst

diff --git a/Documentation/powerpc/elfnote.rst b/Documentation/powerpc/elfnote.rst
new file mode 100644
index 000000000000..2a5c4beeb809
--- /dev/null
+++ b/Documentation/powerpc/elfnote.rst
@@ -0,0 +1,42 @@
+==========================
+ELF Note PowerPC Namespace
+==========================
+
+The PowerPC namespace in an ELF Note of the kernel binary is used to store
+capabilities and information which can be used by a bootloader or userland.
+
+Types and Descriptors
+---------------------
+
+The types to be used with the "PowerPC" namesapce are defined in the
+include/uapi/asm/elfnote.h
+
+	1) PPC_ELFNOTE_CAPABILITIES
+
+Define the capabilities supported/required by the kernel. This type uses a
+bitmap as "descriptor" field. Each bit is described below:
+
+- Ultravisor-capable bit (PowerNV only).
+
+	#define PPCCAP_ULTRAVISOR_BIT (1 << 0)
+
+	Indicate that the powerpc kernel binary knows how to run in an
+	ultravisor-enabled system.
+
+	In an ultravisor-enabled system, some machine resources are now controlled
+	by the ultravisor. If the kernel is not ultravisor-capable, but it ends up
+	being run on a machine with ultravisor, the kernel will probably crash
+	trying to access ultravisor resources. For instance, it may crash in early
+	boot trying to set the partition table entry 0.
+
+	In an ultravisor-enabled system, a bootloader could warn the user or prevent
+   	the kernel from being run if the PowerPC ultravisor capability doesn't exist
+	or the Ultravisor-capable bit is not set.
+
+References
+----------
+
+arch/powerpc/include/asm/elfnote.h
+arch/powerpc/kernel/note.S
+
+
-- 
2.20.1

Re: [PATCH v2 1/2] powerpc: Add PowerPC Capabilities ELF note

[Michael Ellerman]

On Thu, 2019-08-29 at 15:50:20 UTC, "Maxiwell S. Garcia" wrote:
> From: Claudio Carvalho <cclaudio@linux.ibm.com>
> 
> Add the PowerPC name and the PPC_ELFNOTE_CAPABILITIES type in the
> kernel binary ELF note. This type is a bitmap that can be used to
> advertise kernel capabilities to userland.
> 
> This patch also defines PPCCAP_ULTRAVISOR_BIT as being the bit zero.
> 
> Suggested-by: Paul Mackerras <paulus@ozlabs.org>
> Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>
> [ maxiwell: Define the 'PowerPC' type in the elfnote.h ]
> Signed-off-by: Maxiwell S. Garcia <maxiwell@linux.ibm.com>

Series applied to powerpc topic/ppc-kvm, thanks.

https://git.kernel.org/powerpc/c/70ed86f4de5bd74dd2d884dcd2f3275c4cfe665f

cheers