[PATCH v2 0/1] Add XSAVE layout description to Core files for debuggers to support varying XSAVE layouts

[PATCH v2 0/1] Add XSAVE layout description to Core files for debuggers to support varying XSAVE layouts

[Vignesh Balasubramanian]

This patch proposes to add an extra .note section in the corefile to dump the CPUID information of a machine. This is being done to solve the issue of tools like the debuggers having to deal with coredumps from machines with varying XSAVE layouts in spite of having the same XCR0 bits. The new proposed .note section, at this point, consists of an array of records containing the information of each extended feature that is present. This provides details about the offsets and the sizes of the various extended save state components of the machine where the application crash occurred. Requesting a review for this patch.

Please NOTE that this patch has to be applied on top of the patch (https://lore.kernel.org/lkml/874jbt7qz3.fsf@oldenburg3.str.redhat.com/T/).


Vignesh Balasubramanian (1):
  x86/elf: Add a new .note section containing Xfeatures information to
    x86 core files

 arch/x86/Kconfig             |   1 +
 arch/x86/include/asm/elf.h   |  34 +++++++++
 arch/x86/kernel/fpu/xstate.c | 141 +++++++++++++++++++++++++++++++++++
 fs/binfmt_elf.c              |   4 +-
 include/uapi/linux/elf.h     |   1 +
 5 files changed, 179 insertions(+), 2 deletions(-)

-- 
2.34.1

[PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[Vignesh Balasubramanian]

Add a new .note section containing type, size, offset and flags of
every xfeature that is present.

This information will be used by the debuggers to understand the XSAVE
layout of the machine where the core file is dumped, and to read XSAVE
registers, especially during cross-platform debugging.

Some background:

The XSAVE layouts of modern AMD and Intel CPUs differ, especially since
Memory Protection Keys and the AVX-512 features have been inculcated into
the AMD CPUs.
This is since AMD never adopted (and hence never left room in the XSAVE
layout for) the Intel MPX feature. Tools like GDB had assumed a fixed XSAVE
layout matching that of Intel (based on the XCR0 mask).
Hence, the core dumps from AMD CPUs didn't match the known size for the
XCR0 mask. This resulted in GDB and other tools not being able to access
the values of the AVX-512 and PKRU registers on AMD CPUs.
To solve this, an interim solution has been accepted into GDB, and is
already a part of GDB 14, thanks to these series of patches
[ https://sourceware.org/pipermail/gdb-patches/2023-March/198081.html ].
But this patch series depends on heuristics based on the total XSAVE
register set size and the XCR0 mask to infer the layouts of the various
register blocks for core dumps, and hence, is not a foolproof mechanism to
determine the layout of the XSAVE area.

Hence this new core dump note has been proposed as a more sturdy mechanism
to allow GDB/LLDB and other relevant tools to determine the layout of the
XSAVE area of the machine where the corefile was dumped.
The new core dump note (which is being proposed as a per-process .note
section), NT_X86_XSAVE_LAYOUT (0x205) contains an array of structures.
Each structure describes an individual extended feature containing offset,
size and flags (that is obtained through CPUID instruction) in a format
roughly matching the follow C structure:

struct xfeat_component {
       u32 xfeat_type;
       u32 xfeat_sz;
       u32 xfeat_off;
       u32 xfeat_flags;
};

Co-developed-by: Jini Susan George <jinisusan.george@amd.com>
Signed-off-by: Jini Susan George <jinisusan.george@amd.com>
Signed-off-by: Vignesh Balasubramanian <vigbalas@amd.com>
---
v1->v2: Removed kernel internal defn dependency, code improvements

 arch/x86/Kconfig             |   1 +
 arch/x86/include/asm/elf.h   |  34 +++++++++
 arch/x86/kernel/fpu/xstate.c | 141 +++++++++++++++++++++++++++++++++++
 fs/binfmt_elf.c              |   4 +-
 include/uapi/linux/elf.h     |   1 +
 5 files changed, 179 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 928820e61cb5..cc67daab3396 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -105,6 +105,7 @@ config X86
 	select ARCH_HAS_DEBUG_WX
 	select ARCH_HAS_ZONE_DMA_SET if EXPERT
 	select ARCH_HAVE_NMI_SAFE_CMPXCHG
+	select ARCH_HAVE_EXTRA_ELF_NOTES
 	select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
 	select ARCH_MIGHT_HAVE_ACPI_PDC		if ACPI
 	select ARCH_MIGHT_HAVE_PC_PARPORT
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 1fb83d47711f..5952574db64b 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -13,6 +13,40 @@
 #include <asm/auxvec.h>
 #include <asm/fsgsbase.h>
 
+struct xfeat_component {
+	u32 xfeat_type;
+	u32 xfeat_sz;
+	u32 xfeat_off;
+	u32 xfeat_flags;
+} __packed;
+
+_Static_assert(sizeof(struct xfeat_component)%4 == 0, "xfeat_component is not aligned");
+
+enum custom_feature {
+	FEATURE_XSAVE_FP = 0,
+	FEATURE_XSAVE_SSE = 1,
+	FEATURE_XSAVE_YMM = 2,
+	FEATURE_XSAVE_BNDREGS = 3,
+	FEATURE_XSAVE_BNDCSR = 4,
+	FEATURE_XSAVE_OPMASK = 5,
+	FEATURE_XSAVE_ZMM_Hi256 = 6,
+	FEATURE_XSAVE_Hi16_ZMM = 7,
+	FEATURE_XSAVE_PT = 8,
+	FEATURE_XSAVE_PKRU = 9,
+	FEATURE_XSAVE_PASID = 10,
+	FEATURE_XSAVE_CET_USER = 11,
+	FEATURE_XSAVE_CET_SHADOW_STACK = 12,
+	FEATURE_XSAVE_HDC = 13,
+	FEATURE_XSAVE_UINTR = 14,
+	FEATURE_XSAVE_LBR = 15,
+	FEATURE_XSAVE_HWP = 16,
+	FEATURE_XSAVE_XTILE_CFG = 17,
+	FEATURE_XSAVE_XTILE_DATA = 18,
+	FEATURE_MAX,
+	FEATURE_XSAVE_EXTENDED_START = FEATURE_XSAVE_YMM,
+	FEATURE_XSAVE_EXTENDED_END = FEATURE_XSAVE_XTILE_DATA,
+};
+
 typedef unsigned long elf_greg_t;
 
 #define ELF_NGREG (sizeof(struct user_regs_struct) / sizeof(elf_greg_t))
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 33a214b1a4ce..3d1c3c96e34d 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -13,6 +13,7 @@
 #include <linux/seq_file.h>
 #include <linux/proc_fs.h>
 #include <linux/vmalloc.h>
+#include <linux/coredump.h>
 
 #include <asm/fpu/api.h>
 #include <asm/fpu/regset.h>
@@ -87,6 +88,8 @@ static unsigned int xstate_flags[XFEATURE_MAX] __ro_after_init;
 #define XSTATE_FLAG_SUPERVISOR	BIT(0)
 #define XSTATE_FLAG_ALIGNED64	BIT(1)
 
+static const char owner_name[] = "LINUX";
+
 /*
  * Return whether the system supports a given xfeature.
  *
@@ -1837,3 +1840,141 @@ int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
 	return 0;
 }
 #endif /* CONFIG_PROC_PID_ARCH_STATUS */
+
+#ifdef CONFIG_COREDUMP
+static int get_sub_leaf(int custom_xfeat)
+{
+	switch (custom_xfeat) {
+	case FEATURE_XSAVE_YMM:			return XFEATURE_YMM;
+	case FEATURE_XSAVE_BNDREGS:		return XFEATURE_BNDREGS;
+	case FEATURE_XSAVE_BNDCSR:		return XFEATURE_BNDCSR;
+	case FEATURE_XSAVE_OPMASK:		return XFEATURE_OPMASK;
+	case FEATURE_XSAVE_ZMM_Hi256:		return XFEATURE_ZMM_Hi256;
+	case FEATURE_XSAVE_Hi16_ZMM:		return XFEATURE_Hi16_ZMM;
+	case FEATURE_XSAVE_PT:			return XFEATURE_PT_UNIMPLEMENTED_SO_FAR;
+	case FEATURE_XSAVE_PKRU:		return XFEATURE_PKRU;
+	case FEATURE_XSAVE_PASID:		return XFEATURE_PASID;
+	case FEATURE_XSAVE_CET_USER:		return XFEATURE_CET_USER;
+	case FEATURE_XSAVE_CET_SHADOW_STACK:	return XFEATURE_CET_KERNEL_UNUSED;
+	case FEATURE_XSAVE_HDC:			return XFEATURE_RSRVD_COMP_13;
+	case FEATURE_XSAVE_UINTR:		return XFEATURE_RSRVD_COMP_14;
+	case FEATURE_XSAVE_LBR:			return XFEATURE_LBR;
+	case FEATURE_XSAVE_HWP:			return XFEATURE_RSRVD_COMP_16;
+	case FEATURE_XSAVE_XTILE_CFG:		return XFEATURE_XTILE_CFG;
+	case FEATURE_XSAVE_XTILE_DATA:		return XFEATURE_XTILE_DATA;
+	default:
+		pr_warn_ratelimited("Not a valid XSAVE Feature.");
+		return 0;
+	}
+}
+
+/*
+ * Dump type, size, offset and flag values for every xfeature that is present.
+ */
+static int dump_xsave_layout_desc(struct coredump_params *cprm)
+{
+	u32 supported_features = 0;
+	struct xfeat_component xc;
+	u32 eax, ebx, ecx, edx;
+	int num_records = 0;
+	int sub_leaf = 0;
+	int i;
+
+	/* Find supported extended features */
+	cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
+	supported_features = eax;
+
+	for (i = FEATURE_XSAVE_EXTENDED_START;
+			i <= FEATURE_XSAVE_EXTENDED_END; i++) {
+		sub_leaf = get_sub_leaf(i);
+		if (!sub_leaf)
+			continue;
+		if (supported_features & (1U << sub_leaf)) {
+			cpuid_count(XSTATE_CPUID, sub_leaf, &eax, &ebx, &ecx, &edx);
+			xc.xfeat_type = i;
+			xc.xfeat_sz = eax;
+			xc.xfeat_off = ebx;
+			/* Reserved for future use */
+			xc.xfeat_flags = 0;
+
+			if (!dump_emit(cprm, &xc,
+				       sizeof(struct xfeat_component)))
+				return 0;
+			num_records++;
+		}
+	}
+
+	return num_records;
+}
+
+static int get_xsave_desc_size(void)
+{
+	int supported_features = 0;
+	int xfeatures_count = 0;
+	u32 eax, ebx, ecx, edx;
+	int sub_leaf = 0;
+	int i;
+
+	/* Find supported extended features */
+	cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
+	supported_features = eax;
+
+	for (i = FEATURE_XSAVE_EXTENDED_START;
+			i <= FEATURE_XSAVE_EXTENDED_END; i++) {
+		sub_leaf = get_sub_leaf(i);
+		if (!sub_leaf)
+			continue;
+		if (supported_features & (1U << sub_leaf))
+			xfeatures_count++;
+	}
+
+	return xfeatures_count * (sizeof(struct xfeat_component));
+}
+
+int elf_coredump_extra_notes_write(struct coredump_params *cprm)
+{
+	int num_records = 0;
+	struct elf_note en;
+
+	en.n_namesz = sizeof(owner_name);
+	en.n_descsz = get_xsave_desc_size();
+	en.n_type = NT_X86_XSAVE_LAYOUT;
+
+	if (!dump_emit(cprm, &en, sizeof(en)))
+		return 1;
+	if (!dump_emit(cprm, owner_name, en.n_namesz))
+		return 1;
+	if (!dump_align(cprm, 4))
+		return 1;
+
+	num_records = dump_xsave_layout_desc(cprm);
+	if (!num_records) {
+		pr_warn_ratelimited("Error adding XSTATE layout ELF note. XSTATE buffer in the core file will be unparseable.");
+		return 1;
+	}
+
+	/* Total size should be equal to the number of records */
+	if ((sizeof(struct xfeat_component) * num_records) != en.n_descsz) {
+		pr_warn_ratelimited("Error adding XSTATE layout ELF note. The size of the .note section does not match with the total size of the records.");
+		return 1;
+	}
+
+	return 0;
+}
+
+/*
+ * Return the size of new note.
+ */
+int elf_coredump_extra_notes_size(void)
+{
+	int size = 0;
+
+	/* NOTE Header */
+	size += sizeof(struct elf_note);
+	/* name + align */
+	size += roundup(sizeof(owner_name), 4);
+	size += get_xsave_desc_size();
+
+	return size;
+}
+#endif
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 5397b552fbeb..833bcb7e957b 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -2000,7 +2000,7 @@ static int elf_core_dump(struct coredump_params *cprm)
 	{
 		size_t sz = info.size;
 
-		/* For cell spufs */
+		/* For cell spufs and x86 xstate */
 		sz += elf_coredump_extra_notes_size();
 
 		phdr4note = kmalloc(sizeof(*phdr4note), GFP_KERNEL);
@@ -2064,7 +2064,7 @@ static int elf_core_dump(struct coredump_params *cprm)
 	if (!write_note_info(&info, cprm))
 		goto end_coredump;
 
-	/* For cell spufs */
+	/* For cell spufs and x86 xstate */
 	if (elf_coredump_extra_notes_write(cprm))
 		goto end_coredump;
 
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index b54b313bcf07..e30a9b47dc87 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -411,6 +411,7 @@ typedef struct elf64_shdr {
 #define NT_X86_XSTATE	0x202		/* x86 extended state using xsave */
 /* Old binutils treats 0x203 as a CET state */
 #define NT_X86_SHSTK	0x204		/* x86 SHSTK state */
+#define NT_X86_XSAVE_LAYOUT	0x205	/* XSAVE layout description */
 #define NT_S390_HIGH_GPRS	0x300	/* s390 upper register halves */
 #define NT_S390_TIMER	0x301		/* s390 timer register */
 #define NT_S390_TODCMP	0x302		/* s390 TOD clock comparator register */
-- 
2.34.1

Re: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[kernel test robot]

Hi Vignesh,

kernel test robot noticed the following build warnings:

[auto build test WARNING on kees/for-next/execve]
[also build test WARNING on tip/x86/core kees/for-next/pstore kees/for-next/kspp linus/master v6.9-rc7 next-20240507]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Vignesh-Balasubramanian/x86-elf-Add-a-new-note-section-containing-Xfeatures-information-to-x86-core-files/20240507-175615
base:   https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/execve
patch link:    https://lore.kernel.org/r/20240507095330.2674-2-vigbalas%40amd.com
patch subject: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files
config: i386-buildonly-randconfig-006-20240508 (https://download.01.org/0day-ci/archive/20240508/202405080715.hYQ1ae9v-lkp@intel.com/config)
compiler: gcc-8 (Ubuntu 8.4.0-3ubuntu2) 8.4.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240508/202405080715.hYQ1ae9v-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202405080715.hYQ1ae9v-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> arch/x86/kernel/fpu/xstate.c:91:19: warning: 'owner_name' defined but not used [-Wunused-const-variable=]
    static const char owner_name[] = "LINUX";
                      ^~~~~~~~~~
   In file included from include/linux/string.h:369,
                    from arch/x86/include/asm/page_32.h:18,
                    from arch/x86/include/asm/page.h:14,
                    from arch/x86/include/asm/processor.h:20,
                    from arch/x86/include/asm/timex.h:5,
                    from include/linux/timex.h:67,
                    from include/linux/time32.h:13,
                    from include/linux/time.h:60,
                    from include/linux/compat.h:10,
                    from arch/x86/kernel/fpu/xstate.c:8:
   In function 'fortify_memcpy_chk',
       inlined from 'membuf_write.isra.6' at include/linux/regset.h:42:3,
       inlined from '__copy_xstate_to_uabi_buf' at arch/x86/kernel/fpu/xstate.c:1049:2:
   include/linux/fortify-string.h:562:4: warning: call to '__read_overflow2_field' declared with attribute warning: detected read beyond size of field (2nd parameter); maybe use struct_group()?
       __read_overflow2_field(q_size_field, size);
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +/owner_name +91 arch/x86/kernel/fpu/xstate.c

    90	
  > 91	static const char owner_name[] = "LINUX";
    92	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[kernel test robot]

Hi Vignesh,

kernel test robot noticed the following build warnings:

[auto build test WARNING on kees/for-next/execve]
[also build test WARNING on tip/x86/core kees/for-next/pstore kees/for-next/kspp linus/master v6.9-rc7 next-20240507]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Vignesh-Balasubramanian/x86-elf-Add-a-new-note-section-containing-Xfeatures-information-to-x86-core-files/20240507-175615
base:   https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/execve
patch link:    https://lore.kernel.org/r/20240507095330.2674-2-vigbalas%40amd.com
patch subject: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files
config: i386-randconfig-013-20240508 (https://download.01.org/0day-ci/archive/20240508/202405080809.LGYhRYu3-lkp@intel.com/config)
compiler: clang version 18.1.4 (https://github.com/llvm/llvm-project e6c3289804a67ea0bb6a86fadbe454dd93b8d855)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240508/202405080809.LGYhRYu3-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202405080809.LGYhRYu3-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> arch/x86/kernel/fpu/xstate.c:91:19: warning: unused variable 'owner_name' [-Wunused-const-variable]
      91 | static const char owner_name[] = "LINUX";
         |                   ^~~~~~~~~~
   1 warning generated.

Kconfig warnings: (for reference only)
   WARNING: unmet direct dependencies detected for DRM_I915_DEBUG_GEM
   Depends on [n]: HAS_IOMEM [=y] && DRM_I915 [=m] && EXPERT [=y] && DRM_I915_WERROR [=n]
   Selected by [m]:
   - DRM_I915_DEBUG [=y] && HAS_IOMEM [=y] && DRM_I915 [=m] && EXPERT [=y] && !COMPILE_TEST [=n]


vim +/owner_name +91 arch/x86/kernel/fpu/xstate.c

    90	
  > 91	static const char owner_name[] = "LINUX";
    92	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[Kees Cook]

On Tue, May 07, 2024 at 03:23:31PM +0530, Vignesh Balasubramanian wrote:
> Add a new .note section containing type, size, offset and flags of
> every xfeature that is present.
> 
> This information will be used by the debuggers to understand the XSAVE
> layout of the machine where the core file is dumped, and to read XSAVE
> registers, especially during cross-platform debugging.
> 
> Some background:
> 
> The XSAVE layouts of modern AMD and Intel CPUs differ, especially since
> Memory Protection Keys and the AVX-512 features have been inculcated into
> the AMD CPUs.
> This is since AMD never adopted (and hence never left room in the XSAVE
> layout for) the Intel MPX feature. Tools like GDB had assumed a fixed XSAVE
> layout matching that of Intel (based on the XCR0 mask).
> Hence, the core dumps from AMD CPUs didn't match the known size for the
> XCR0 mask. This resulted in GDB and other tools not being able to access
> the values of the AVX-512 and PKRU registers on AMD CPUs.
> To solve this, an interim solution has been accepted into GDB, and is
> already a part of GDB 14, thanks to these series of patches
> [ https://sourceware.org/pipermail/gdb-patches/2023-March/198081.html ].
> But this patch series depends on heuristics based on the total XSAVE
> register set size and the XCR0 mask to infer the layouts of the various
> register blocks for core dumps, and hence, is not a foolproof mechanism to
> determine the layout of the XSAVE area.
> 
> Hence this new core dump note has been proposed as a more sturdy mechanism
> to allow GDB/LLDB and other relevant tools to determine the layout of the
> XSAVE area of the machine where the corefile was dumped.
> The new core dump note (which is being proposed as a per-process .note
> section), NT_X86_XSAVE_LAYOUT (0x205) contains an array of structures.
> Each structure describes an individual extended feature containing offset,
> size and flags (that is obtained through CPUID instruction) in a format
> roughly matching the follow C structure:
> 
> struct xfeat_component {
>        u32 xfeat_type;
>        u32 xfeat_sz;
>        u32 xfeat_off;
>        u32 xfeat_flags;
> };
> 
> Co-developed-by: Jini Susan George <jinisusan.george@amd.com>
> Signed-off-by: Jini Susan George <jinisusan.george@amd.com>
> Signed-off-by: Vignesh Balasubramanian <vigbalas@amd.com>
> ---
> v1->v2: Removed kernel internal defn dependency, code improvements
> 
>  arch/x86/Kconfig             |   1 +
>  arch/x86/include/asm/elf.h   |  34 +++++++++
>  arch/x86/kernel/fpu/xstate.c | 141 +++++++++++++++++++++++++++++++++++
>  fs/binfmt_elf.c              |   4 +-
>  include/uapi/linux/elf.h     |   1 +
>  5 files changed, 179 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 928820e61cb5..cc67daab3396 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -105,6 +105,7 @@ config X86
>  	select ARCH_HAS_DEBUG_WX
>  	select ARCH_HAS_ZONE_DMA_SET if EXPERT
>  	select ARCH_HAVE_NMI_SAFE_CMPXCHG
> +	select ARCH_HAVE_EXTRA_ELF_NOTES
>  	select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
>  	select ARCH_MIGHT_HAVE_ACPI_PDC		if ACPI
>  	select ARCH_MIGHT_HAVE_PC_PARPORT
> diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
> index 1fb83d47711f..5952574db64b 100644
> --- a/arch/x86/include/asm/elf.h
> +++ b/arch/x86/include/asm/elf.h
> @@ -13,6 +13,40 @@
>  #include <asm/auxvec.h>
>  #include <asm/fsgsbase.h>
>  
> +struct xfeat_component {
> +	u32 xfeat_type;
> +	u32 xfeat_sz;
> +	u32 xfeat_off;
> +	u32 xfeat_flags;
> +} __packed;
> +
> +_Static_assert(sizeof(struct xfeat_component)%4 == 0, "xfeat_component is not aligned");
> +
> +enum custom_feature {
> +	FEATURE_XSAVE_FP = 0,
> +	FEATURE_XSAVE_SSE = 1,
> +	FEATURE_XSAVE_YMM = 2,
> +	FEATURE_XSAVE_BNDREGS = 3,
> +	FEATURE_XSAVE_BNDCSR = 4,
> +	FEATURE_XSAVE_OPMASK = 5,
> +	FEATURE_XSAVE_ZMM_Hi256 = 6,
> +	FEATURE_XSAVE_Hi16_ZMM = 7,
> +	FEATURE_XSAVE_PT = 8,
> +	FEATURE_XSAVE_PKRU = 9,
> +	FEATURE_XSAVE_PASID = 10,
> +	FEATURE_XSAVE_CET_USER = 11,
> +	FEATURE_XSAVE_CET_SHADOW_STACK = 12,
> +	FEATURE_XSAVE_HDC = 13,
> +	FEATURE_XSAVE_UINTR = 14,
> +	FEATURE_XSAVE_LBR = 15,
> +	FEATURE_XSAVE_HWP = 16,
> +	FEATURE_XSAVE_XTILE_CFG = 17,
> +	FEATURE_XSAVE_XTILE_DATA = 18,
> +	FEATURE_MAX,
> +	FEATURE_XSAVE_EXTENDED_START = FEATURE_XSAVE_YMM,
> +	FEATURE_XSAVE_EXTENDED_END = FEATURE_XSAVE_XTILE_DATA,
> +};
> +
>  typedef unsigned long elf_greg_t;
>  
>  #define ELF_NGREG (sizeof(struct user_regs_struct) / sizeof(elf_greg_t))
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index 33a214b1a4ce..3d1c3c96e34d 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -13,6 +13,7 @@
>  #include <linux/seq_file.h>
>  #include <linux/proc_fs.h>
>  #include <linux/vmalloc.h>
> +#include <linux/coredump.h>
>  
>  #include <asm/fpu/api.h>
>  #include <asm/fpu/regset.h>
> @@ -87,6 +88,8 @@ static unsigned int xstate_flags[XFEATURE_MAX] __ro_after_init;
>  #define XSTATE_FLAG_SUPERVISOR	BIT(0)
>  #define XSTATE_FLAG_ALIGNED64	BIT(1)
>  
> +static const char owner_name[] = "LINUX";

This needs to move under the CONFIG_COREDUMP below (so says the build
bots).

> +
>  /*
>   * Return whether the system supports a given xfeature.
>   *
> @@ -1837,3 +1840,141 @@ int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
>  	return 0;
>  }
>  #endif /* CONFIG_PROC_PID_ARCH_STATUS */
> +
> +#ifdef CONFIG_COREDUMP
> +static int get_sub_leaf(int custom_xfeat)

Why is this "int"? I don't imagine there are negative features?

> +{
> +	switch (custom_xfeat) {
> +	case FEATURE_XSAVE_YMM:			return XFEATURE_YMM;
> +	case FEATURE_XSAVE_BNDREGS:		return XFEATURE_BNDREGS;
> +	case FEATURE_XSAVE_BNDCSR:		return XFEATURE_BNDCSR;
> +	case FEATURE_XSAVE_OPMASK:		return XFEATURE_OPMASK;
> +	case FEATURE_XSAVE_ZMM_Hi256:		return XFEATURE_ZMM_Hi256;
> +	case FEATURE_XSAVE_Hi16_ZMM:		return XFEATURE_Hi16_ZMM;
> +	case FEATURE_XSAVE_PT:			return XFEATURE_PT_UNIMPLEMENTED_SO_FAR;
> +	case FEATURE_XSAVE_PKRU:		return XFEATURE_PKRU;
> +	case FEATURE_XSAVE_PASID:		return XFEATURE_PASID;
> +	case FEATURE_XSAVE_CET_USER:		return XFEATURE_CET_USER;
> +	case FEATURE_XSAVE_CET_SHADOW_STACK:	return XFEATURE_CET_KERNEL_UNUSED;
> +	case FEATURE_XSAVE_HDC:			return XFEATURE_RSRVD_COMP_13;
> +	case FEATURE_XSAVE_UINTR:		return XFEATURE_RSRVD_COMP_14;
> +	case FEATURE_XSAVE_LBR:			return XFEATURE_LBR;
> +	case FEATURE_XSAVE_HWP:			return XFEATURE_RSRVD_COMP_16;
> +	case FEATURE_XSAVE_XTILE_CFG:		return XFEATURE_XTILE_CFG;
> +	case FEATURE_XSAVE_XTILE_DATA:		return XFEATURE_XTILE_DATA;
> +	default:
> +		pr_warn_ratelimited("Not a valid XSAVE Feature.");

This isn't very friendly; it's keeping secrets about the unknown value. :)
Also it's missing a newline. How about:

		pr_warn_ratelimited("Not a known XSAVE Feature: %u\n",
				    custom_xfeat);

> +		return 0;
> +	}
> +}
> +
> +/*
> + * Dump type, size, offset and flag values for every xfeature that is present.
> + */
> +static int dump_xsave_layout_desc(struct coredump_params *cprm)
> +{
> +	u32 supported_features = 0;
> +	struct xfeat_component xc;
> +	u32 eax, ebx, ecx, edx;
> +	int num_records = 0;
> +	int sub_leaf = 0;
> +	int i;
> +
> +	/* Find supported extended features */
> +	cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
> +	supported_features = eax;
> +
> +	for (i = FEATURE_XSAVE_EXTENDED_START;
> +			i <= FEATURE_XSAVE_EXTENDED_END; i++) {
> +		sub_leaf = get_sub_leaf(i);
> +		if (!sub_leaf)
> +			continue;
> +		if (supported_features & (1U << sub_leaf)) {
> +			cpuid_count(XSTATE_CPUID, sub_leaf, &eax, &ebx, &ecx, &edx);
> +			xc.xfeat_type = i;
> +			xc.xfeat_sz = eax;
> +			xc.xfeat_off = ebx;
> +			/* Reserved for future use */
> +			xc.xfeat_flags = 0;
> +
> +			if (!dump_emit(cprm, &xc,
> +				       sizeof(struct xfeat_component)))
> +				return 0;
> +			num_records++;
> +		}
> +	}
> +
> +	return num_records;
> +}
> +
> +static int get_xsave_desc_size(void)

This can return u32: never negative.

> +{
> +	int supported_features = 0;
> +	int xfeatures_count = 0;
> +	u32 eax, ebx, ecx, edx;
> +	int sub_leaf = 0;
> +	int i;

"i" can be u32 and then we can fix the get_sub_leaf() arg type.

> +
> +	/* Find supported extended features */
> +	cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
> +	supported_features = eax;
> +
> +	for (i = FEATURE_XSAVE_EXTENDED_START;
> +			i <= FEATURE_XSAVE_EXTENDED_END; i++) {
> +		sub_leaf = get_sub_leaf(i);
> +		if (!sub_leaf)
> +			continue;
> +		if (supported_features & (1U << sub_leaf))
> +			xfeatures_count++;
> +	}
> +
> +	return xfeatures_count * (sizeof(struct xfeat_component));
> +}
> +
> +int elf_coredump_extra_notes_write(struct coredump_params *cprm)
> +{
> +	int num_records = 0;
> +	struct elf_note en;
> +
> +	en.n_namesz = sizeof(owner_name);
> +	en.n_descsz = get_xsave_desc_size();
> +	en.n_type = NT_X86_XSAVE_LAYOUT;
> +
> +	if (!dump_emit(cprm, &en, sizeof(en)))
> +		return 1;
> +	if (!dump_emit(cprm, owner_name, en.n_namesz))
> +		return 1;
> +	if (!dump_align(cprm, 4))
> +		return 1;
> +
> +	num_records = dump_xsave_layout_desc(cprm);
> +	if (!num_records) {
> +		pr_warn_ratelimited("Error adding XSTATE layout ELF note. XSTATE buffer in the core file will be unparseable.");

Missing trailing newline.

> +		return 1;
> +	}
> +
> +	/* Total size should be equal to the number of records */
> +	if ((sizeof(struct xfeat_component) * num_records) != en.n_descsz) {
> +		pr_warn_ratelimited("Error adding XSTATE layout ELF note. The size of the .note section does not match with the total size of the records.");

Same.

> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * Return the size of new note.
> + */
> +int elf_coredump_extra_notes_size(void)
> +{
> +	int size = 0;
> +
> +	/* NOTE Header */
> +	size += sizeof(struct elf_note);
> +	/* name + align */
> +	size += roundup(sizeof(owner_name), 4);
> +	size += get_xsave_desc_size();
> +
> +	return size;
> +}
> +#endif

Since it's a long if/endif, add: /* CONFIG_COREDUMP */ after the endif
here.

> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 5397b552fbeb..833bcb7e957b 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -2000,7 +2000,7 @@ static int elf_core_dump(struct coredump_params *cprm)
>  	{
>  		size_t sz = info.size;
>  
> -		/* For cell spufs */
> +		/* For cell spufs and x86 xstate */
>  		sz += elf_coredump_extra_notes_size();
>  
>  		phdr4note = kmalloc(sizeof(*phdr4note), GFP_KERNEL);
> @@ -2064,7 +2064,7 @@ static int elf_core_dump(struct coredump_params *cprm)
>  	if (!write_note_info(&info, cprm))
>  		goto end_coredump;
>  
> -	/* For cell spufs */
> +	/* For cell spufs and x86 xstate */
>  	if (elf_coredump_extra_notes_write(cprm))
>  		goto end_coredump;
>  
> diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
> index b54b313bcf07..e30a9b47dc87 100644
> --- a/include/uapi/linux/elf.h
> +++ b/include/uapi/linux/elf.h
> @@ -411,6 +411,7 @@ typedef struct elf64_shdr {
>  #define NT_X86_XSTATE	0x202		/* x86 extended state using xsave */
>  /* Old binutils treats 0x203 as a CET state */
>  #define NT_X86_SHSTK	0x204		/* x86 SHSTK state */
> +#define NT_X86_XSAVE_LAYOUT	0x205	/* XSAVE layout description */
>  #define NT_S390_HIGH_GPRS	0x300	/* s390 upper register halves */
>  #define NT_S390_TIMER	0x301		/* s390 timer register */
>  #define NT_S390_TODCMP	0x302		/* s390 TOD clock comparator register */
> -- 
> 2.34.1
> 

Otherwise looks good. I'd like to see feedback from Intel folks too.

Thanks for working on this!

-Kees

-- 
Kees Cook

Re: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[Thomas Gleixner]

On Tue, May 07 2024 at 15:23, Vignesh Balasubramanian wrote:
> +struct xfeat_component {
> +	u32 xfeat_type;
> +	u32 xfeat_sz;
> +	u32 xfeat_off;
> +	u32 xfeat_flags;
> +} __packed;

Why repeating xfeat_ for all member names?

    u32       type;
    u32       size;
    u32       offset;
    u32       flags;

is sufficient and obvious, no?

> +enum custom_feature {
> +	FEATURE_XSAVE_FP = 0,
> +	FEATURE_XSAVE_SSE = 1,
> +	FEATURE_XSAVE_YMM = 2,
> +	FEATURE_XSAVE_BNDREGS = 3,
> +	FEATURE_XSAVE_BNDCSR = 4,
> +	FEATURE_XSAVE_OPMASK = 5,
> +	FEATURE_XSAVE_ZMM_Hi256 = 6,
> +	FEATURE_XSAVE_Hi16_ZMM = 7,
> +	FEATURE_XSAVE_PT = 8,
> +	FEATURE_XSAVE_PKRU = 9,
> +	FEATURE_XSAVE_PASID = 10,
> +	FEATURE_XSAVE_CET_USER = 11,
> +	FEATURE_XSAVE_CET_SHADOW_STACK = 12,
> +	FEATURE_XSAVE_HDC = 13,
> +	FEATURE_XSAVE_UINTR = 14,
> +	FEATURE_XSAVE_LBR = 15,
> +	FEATURE_XSAVE_HWP = 16,
> +	FEATURE_XSAVE_XTILE_CFG = 17,
> +	FEATURE_XSAVE_XTILE_DATA = 18,
> +	FEATURE_MAX,
> +	FEATURE_XSAVE_EXTENDED_START = FEATURE_XSAVE_YMM,
> +	FEATURE_XSAVE_EXTENDED_END = FEATURE_XSAVE_XTILE_DATA,
> +};

Why can't this use the existing 'enum xfeature' which is providing
exactly the same information already?

> +#ifdef CONFIG_COREDUMP
> +static int get_sub_leaf(int custom_xfeat)
> +{
> +	switch (custom_xfeat) {
> +	case FEATURE_XSAVE_YMM:			return XFEATURE_YMM;
> +	case FEATURE_XSAVE_BNDREGS:		return XFEATURE_BNDREGS;
> +	case FEATURE_XSAVE_BNDCSR:		return XFEATURE_BNDCSR;
> +	case FEATURE_XSAVE_OPMASK:		return XFEATURE_OPMASK;
> +	case FEATURE_XSAVE_ZMM_Hi256:		return XFEATURE_ZMM_Hi256;
> +	case FEATURE_XSAVE_Hi16_ZMM:		return XFEATURE_Hi16_ZMM;
> +	case FEATURE_XSAVE_PT:			return XFEATURE_PT_UNIMPLEMENTED_SO_FAR;
> +	case FEATURE_XSAVE_PKRU:		return XFEATURE_PKRU;
> +	case FEATURE_XSAVE_PASID:		return XFEATURE_PASID;
> +	case FEATURE_XSAVE_CET_USER:		return XFEATURE_CET_USER;
> +	case FEATURE_XSAVE_CET_SHADOW_STACK:	return XFEATURE_CET_KERNEL_UNUSED;
> +	case FEATURE_XSAVE_HDC:			return XFEATURE_RSRVD_COMP_13;
> +	case FEATURE_XSAVE_UINTR:		return XFEATURE_RSRVD_COMP_14;
> +	case FEATURE_XSAVE_LBR:			return XFEATURE_LBR;
> +	case FEATURE_XSAVE_HWP:			return XFEATURE_RSRVD_COMP_16;
> +	case FEATURE_XSAVE_XTILE_CFG:		return XFEATURE_XTILE_CFG;
> +	case FEATURE_XSAVE_XTILE_DATA:		return XFEATURE_XTILE_DATA;
> +	default:
> +		pr_warn_ratelimited("Not a valid XSAVE Feature.");
> +		return 0;
> +	}
> +}

This function then maps the identical enums one to one. The only actual
"functionality" is the default case and that's completely pointless.

> +/*
> + * Dump type, size, offset and flag values for every xfeature that is present.
> + */
> +static int dump_xsave_layout_desc(struct coredump_params *cprm)
> +{
> +	u32 supported_features = 0;
> +	struct xfeat_component xc;
> +	u32 eax, ebx, ecx, edx;
> +	int num_records = 0;
> +	int sub_leaf = 0;
> +	int i;
> +
> +	/* Find supported extended features */
> +	cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
> +	supported_features = eax;

Why does this need to re-evaluate CPUID instead of just using the
existing fpu_user_cfg.max_features?

> +	for (i = FEATURE_XSAVE_EXTENDED_START;
> +			i <= FEATURE_XSAVE_EXTENDED_END; i++) {

Please use the full 100 character line width.

> +		sub_leaf = get_sub_leaf(i);
> +		if (!sub_leaf)
> +			continue;
> +		if (supported_features & (1U << sub_leaf)) {
> +			cpuid_count(XSTATE_CPUID, sub_leaf, &eax, &ebx, &ecx, &edx);
> +			xc.xfeat_type = i;
> +			xc.xfeat_sz = eax;
> +			xc.xfeat_off = ebx;
> +			/* Reserved for future use */
> +			xc.xfeat_flags = 0;
> +
> +			if (!dump_emit(cprm, &xc,
> +				       sizeof(struct xfeat_component)))

sizeof(xc), no?

> +				return 0;
> +			num_records++;
> +		}
> +	}

This whole thing can be written as:

	for_each_extended_xfeature(i, fpu_user_cfg.max_features) {
		struct xfeat_component xc = {
                	.type	= i,
                        .size	= xstate_sizes[i],
                        .offset	= xstate_offsets[i],
		};

		if (!dump_emit(cprm, &xc, sizeof(xc)))
			return 0;
                num_records++;
	}

It omits the features which are supported by the CPU, but not enabled by
the kernel. That's perfectly fine because:

  1) the corresponding xfeature bits of those component in the actual
     XSAVE dump are guaranteed to be zero

  2) the corresponding regions in the actual XSAVE dump are zeroed

So there is absolutely no point in having notes for the not enabled
features at all.

Hmm?

> +
> +	return num_records;
> +}
> +
> +static int get_xsave_desc_size(void)
> +{
> +	int supported_features = 0;
> +	int xfeatures_count = 0;
> +	u32 eax, ebx, ecx, edx;
> +	int sub_leaf = 0;
> +	int i;
> +
> +	/* Find supported extended features */
> +	cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
> +	supported_features = eax;
> +
> +	for (i = FEATURE_XSAVE_EXTENDED_START;
> +			i <= FEATURE_XSAVE_EXTENDED_END; i++) {
> +		sub_leaf = get_sub_leaf(i);
> +		if (!sub_leaf)
> +			continue;
> +		if (supported_features & (1U << sub_leaf))
> +			xfeatures_count++;
> +	}
> +	return xfeatures_count * (sizeof(struct xfeat_component));

Then this can be replaced by:

	int i, cnt = 0;

	for_each_extended_xfeature(i, fpu_user_cfg.max_features)
        	cnt++;

        return cnt * sizeof(struct xfeat_component);

In fact the number of extended features can be calculated once during
boot during xstate initialization.

No?

> +}
> +
> +int elf_coredump_extra_notes_write(struct coredump_params *cprm)
> +{
> +	int num_records = 0;
> +	struct elf_note en;
> +
> +	en.n_namesz = sizeof(owner_name);
> +	en.n_descsz = get_xsave_desc_size();
> +	en.n_type = NT_X86_XSAVE_LAYOUT;
> +
> +	if (!dump_emit(cprm, &en, sizeof(en)))
> +		return 1;
> +	if (!dump_emit(cprm, owner_name, en.n_namesz))
> +		return 1;
> +	if (!dump_align(cprm, 4))
> +		return 1;
> +
> +	num_records = dump_xsave_layout_desc(cprm);
> +	if (!num_records) {
> +		pr_warn_ratelimited("Error adding XSTATE layout ELF note. XSTATE buffer in the core file will be unparseable.");
> +		return 1;

This is going to trigger on all systems which do not support XSAVE. So
why emitting this note in the first place on such systems?

The function should have

	if (!fpu_kernel_cfg.max_features)
        	return 0;

right at the beginning.

Aside of that, these warnings are pointless noise in the case that
dump_emit() caused the function to return early. Dumps can be truncated.

> +/*
> + * Return the size of new note.

Which new note? This is extra notes, no?

> + */
> +int elf_coredump_extra_notes_size(void)
> +{
> +	int size = 0;

	int size;

> +
> +	/* NOTE Header */

  Note header ?

> +	size += sizeof(struct elf_note);

	size = ....

> +	/* name + align */

  Name plus alignment to 4 bytes ?

> +	size += roundup(sizeof(owner_name), 4);
> +	size += get_xsave_desc_size();
> +
> +	return size;
> +}

And like the write function this wants:

	if (!fpu_kernel_cfg.max_features)
        	return 0;

at the beginning. No point in emitting useless notes and headers.

Thanks,

        tglx

Re: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[Balasubrmanian, Vignesh]

On 5/8/2024 6:32 PM, Thomas Gleixner wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
>
>
> On Tue, May 07 2024 at 15:23, Vignesh Balasubramanian wrote:
>> +struct xfeat_component {
>> +     u32 xfeat_type;
>> +     u32 xfeat_sz;
>> +     u32 xfeat_off;
>> +     u32 xfeat_flags;
>> +} __packed;
> Why repeating xfeat_ for all member names?
>
>      u32       type;
>      u32       size;
>      u32       offset;
>      u32       flags;
>
> is sufficient and obvious, no?
>
>> +enum custom_feature {
>> +     FEATURE_XSAVE_FP = 0,
>> +     FEATURE_XSAVE_SSE = 1,
>> +     FEATURE_XSAVE_YMM = 2,
>> +     FEATURE_XSAVE_BNDREGS = 3,
>> +     FEATURE_XSAVE_BNDCSR = 4,
>> +     FEATURE_XSAVE_OPMASK = 5,
>> +     FEATURE_XSAVE_ZMM_Hi256 = 6,
>> +     FEATURE_XSAVE_Hi16_ZMM = 7,
>> +     FEATURE_XSAVE_PT = 8,
>> +     FEATURE_XSAVE_PKRU = 9,
>> +     FEATURE_XSAVE_PASID = 10,
>> +     FEATURE_XSAVE_CET_USER = 11,
>> +     FEATURE_XSAVE_CET_SHADOW_STACK = 12,
>> +     FEATURE_XSAVE_HDC = 13,
>> +     FEATURE_XSAVE_UINTR = 14,
>> +     FEATURE_XSAVE_LBR = 15,
>> +     FEATURE_XSAVE_HWP = 16,
>> +     FEATURE_XSAVE_XTILE_CFG = 17,
>> +     FEATURE_XSAVE_XTILE_DATA = 18,
>> +     FEATURE_MAX,
>> +     FEATURE_XSAVE_EXTENDED_START = FEATURE_XSAVE_YMM,
>> +     FEATURE_XSAVE_EXTENDED_END = FEATURE_XSAVE_XTILE_DATA,
>> +};
> Why can't this use the existing 'enum xfeature' which is providing
> exactly the same information already?
First version of patch was similar to what you mentioned here and other 
review comments to use existing kernel definitions.
https://lore.kernel.org/linux-mm/20240314112359.50713-1-vigbalas@amd.com/T/

As per the review comment 
https://lore.kernel.org/linux-mm/20240314162954.GAZfMmAnYQoRjRbRzc@fat_crate.local/ 
, modified the patch to be a independent of kernel internal definitions.
Though this enum and below function  "get_sub_leaf" are not useful now,  
it will be required when we extend for a new/different features.

Please let  us know your suggestions.

I will fix all other review comments in my next version.

>> +#ifdef CONFIG_COREDUMP
>> +static int get_sub_leaf(int custom_xfeat)
>> +{
>> +     switch (custom_xfeat) {
>> +     case FEATURE_XSAVE_YMM:                 return XFEATURE_YMM;
>> +     case FEATURE_XSAVE_BNDREGS:             return XFEATURE_BNDREGS;
>> +     case FEATURE_XSAVE_BNDCSR:              return XFEATURE_BNDCSR;
>> +     case FEATURE_XSAVE_OPMASK:              return XFEATURE_OPMASK;
>> +     case FEATURE_XSAVE_ZMM_Hi256:           return XFEATURE_ZMM_Hi256;
>> +     case FEATURE_XSAVE_Hi16_ZMM:            return XFEATURE_Hi16_ZMM;
>> +     case FEATURE_XSAVE_PT:                  return XFEATURE_PT_UNIMPLEMENTED_SO_FAR;
>> +     case FEATURE_XSAVE_PKRU:                return XFEATURE_PKRU;
>> +     case FEATURE_XSAVE_PASID:               return XFEATURE_PASID;
>> +     case FEATURE_XSAVE_CET_USER:            return XFEATURE_CET_USER;
>> +     case FEATURE_XSAVE_CET_SHADOW_STACK:    return XFEATURE_CET_KERNEL_UNUSED;
>> +     case FEATURE_XSAVE_HDC:                 return XFEATURE_RSRVD_COMP_13;
>> +     case FEATURE_XSAVE_UINTR:               return XFEATURE_RSRVD_COMP_14;
>> +     case FEATURE_XSAVE_LBR:                 return XFEATURE_LBR;
>> +     case FEATURE_XSAVE_HWP:                 return XFEATURE_RSRVD_COMP_16;
>> +     case FEATURE_XSAVE_XTILE_CFG:           return XFEATURE_XTILE_CFG;
>> +     case FEATURE_XSAVE_XTILE_DATA:          return XFEATURE_XTILE_DATA;
>> +     default:
>> +             pr_warn_ratelimited("Not a valid XSAVE Feature.");
>> +             return 0;
>> +     }
>> +}
> This function then maps the identical enums one to one. The only actual
> "functionality" is the default case and that's completely pointless.
thanks,
vigneshbalu.

Re: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[Borislav Petkov]

On Wed, May 22, 2024 at 06:42:55PM +0530, Balasubrmanian, Vignesh wrote:
> > > +enum custom_feature {
> > > +     FEATURE_XSAVE_FP = 0,
> > > +     FEATURE_XSAVE_SSE = 1,
> > > +     FEATURE_XSAVE_YMM = 2,
> > > +     FEATURE_XSAVE_BNDREGS = 3,
> > > +     FEATURE_XSAVE_BNDCSR = 4,
> > > +     FEATURE_XSAVE_OPMASK = 5,
> > > +     FEATURE_XSAVE_ZMM_Hi256 = 6,
> > > +     FEATURE_XSAVE_Hi16_ZMM = 7,
> > > +     FEATURE_XSAVE_PT = 8,
> > > +     FEATURE_XSAVE_PKRU = 9,
> > > +     FEATURE_XSAVE_PASID = 10,
> > > +     FEATURE_XSAVE_CET_USER = 11,
> > > +     FEATURE_XSAVE_CET_SHADOW_STACK = 12,
> > > +     FEATURE_XSAVE_HDC = 13,
> > > +     FEATURE_XSAVE_UINTR = 14,
> > > +     FEATURE_XSAVE_LBR = 15,
> > > +     FEATURE_XSAVE_HWP = 16,
> > > +     FEATURE_XSAVE_XTILE_CFG = 17,
> > > +     FEATURE_XSAVE_XTILE_DATA = 18,
> > > +     FEATURE_MAX,
> > > +     FEATURE_XSAVE_EXTENDED_START = FEATURE_XSAVE_YMM,
> > > +     FEATURE_XSAVE_EXTENDED_END = FEATURE_XSAVE_XTILE_DATA,
> > > +};
> > Why can't this use the existing 'enum xfeature' which is providing
> > exactly the same information already?
> First version of patch was similar to what you mentioned here and other
> review comments to use existing kernel definitions.
> https://lore.kernel.org/linux-mm/20240314112359.50713-1-vigbalas@amd.com/T/
> 
> As per the review comment https://lore.kernel.org/linux-mm/20240314162954.GAZfMmAnYQoRjRbRzc@fat_crate.local/
> , modified the patch to be a independent of kernel internal definitions.
> Though this enum and below function  "get_sub_leaf" are not useful now,  it
> will be required when we extend for a new/different features.

No, Thomas' sugggestion is to use the existing xfeature enum - not
define the same thing again.

Why do you need that enum custom_feature thing if you can use

/*
 * List of XSAVE features Linux knows about:
 */
enum xfeature {

from arch/x86/include/asm/fpu/types.h

?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[Borislav Petkov]

On Thu, May 23, 2024 at 11:57:00AM +0530, Balasubrmanian, Vignesh wrote:
> Currently, this enum is the same as XSAVE, but when we add other features, this
> enum might have a different value of the XSAVE features and can be modified
> without disturbing the existing kernel code.

We will do that when we cross that bridge, right?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[Balasubrmanian, Vignesh]

On 5/23/2024 8:15 PM, Borislav Petkov wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
>
>
> On Thu, May 23, 2024 at 11:57:00AM +0530, Balasubrmanian, Vignesh wrote:
>> Currently, this enum is the same as XSAVE, but when we add other features, this
>> enum might have a different value of the XSAVE features and can be modified
>> without disturbing the existing kernel code.
> We will do that when we cross that bridge, right?

I am struggling to interpret.
If we can add a new enum only when we extend, then as Thomas suggested 
can we use other kernel variables as in the first version of the patch 
until we extend for other/new features?

thanks,
vigneshbalu.

>
> --
> Regards/Gruss,
>      Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v2 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files

[Borislav Petkov]

On Sun, May 26, 2024 at 10:24:41AM +0530, Balasubrmanian, Vignesh wrote:
> If we can add a new enum only when we extend, then as Thomas suggested can
> we use other kernel variables as in the first version of the patch until we
> extend for other/new features?

I assume by "other kernel variables" you mean CPUID?

If so, can you change the layout of your buffer once you export it to
userspace?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette