[PATCH 1/8] binfmt_elf: Extract .note.gnu.property from an ELF file

From: Dave Martin
Date: Fri May 24 2019 - 06:29:24 EST

Next message: Dave Martin: "[PATCH 2/8] mm: Reserve asm-generic prot flag 0x10 for arch use"
Previous message: Enric Balletbo i Serra: "Re: [PATCH v4 3/3] platform/chrome: cros_ec_spi: Request the SPI thread be realtime"
In reply to: Dave Martin: "[PATCH 0/8] arm64: ARMv8.5-A: Branch Target Identification support"
Next in thread: Dave Martin: "[PATCH 2/8] mm: Reserve asm-generic prot flag 0x10 for arch use"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>

An ELF file's .note.gnu.property indicates features the executable file
can support. For example, the property GNU_PROPERTY_X86_FEATURE_1_AND
indicates the file supports GNU_PROPERTY_X86_FEATURE_1_IBT and/or
GNU_PROPERTY_X86_FEATURE_1_SHSTK.

This patch was part of the Control-flow Enforcement series; the original
patch is here: https://lkml.org/lkml/2018/11/20/205. Dave Martin responded
that ARM recently introduced new features to NT_GNU_PROPERTY_TYPE_0 with
properties closely modelled on GNU_PROPERTY_X86_FEATURE_1_AND, and it is
logical to split out the generic part. Here it is.

With this patch, if an arch needs to setup features from ELF properties,
it needs CONFIG_ARCH_USE_GNU_PROPERTY to be set, and a specific
arch_setup_property().

For example, for X86_64:

int arch_setup_property(void *ehdr, void *phdr, struct file *f, bool inter)
{
int r;
uint32_t property;

r = get_gnu_property(ehdr, phdr, f, GNU_PROPERTY_X86_FEATURE_1_AND,
&property);
...
}

Signed-off-by: H.J. Lu <hjl.tools@xxxxxxxxx>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx> [rebase to v5.2-rc1]

---

Notes from Dave:

* For arm64 at least, I'm hoping we can rely on the PT_GNU_PROPERTY
program header to find the program properties. If this works for
x86 too, I think the code could be simplified considerably.

Ideally we would always use that: having to exhaustively search
all the notes in the image instead doesn't feel like the right design
IMHO.

This needs further discussion, and I make no attempt to address it
for now.
---
fs/Kconfig.binfmt | 4 +
fs/Makefile | 1 +
fs/binfmt_elf.c | 13 ++
fs/gnu_property.c | 363 +++++++++++++++++++++++++++++++++++++++++++++++
include/linux/elf.h | 12 ++
include/uapi/linux/elf.h | 8 ++
6 files changed, 401 insertions(+)
create mode 100644 fs/gnu_property.c

diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index b795f8d..175a1f5 100644
--- a/fs/Kconfig.binfmt
+++ b/fs/Kconfig.binfmt
@@ -35,6 +35,10 @@ config COMPAT_BINFMT_ELF
config ARCH_BINFMT_ELF_STATE
bool

+config ARCH_USE_GNU_PROPERTY
+ bool
+ depends on 64BIT
+
config BINFMT_ELF_FDPIC
bool "Kernel support for FDPIC ELF binaries"
default y if !BINFMT_ELF
diff --git a/fs/Makefile b/fs/Makefile
index c9aea23..b69f18c 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -44,6 +44,7 @@ obj-$(CONFIG_BINFMT_ELF) += binfmt_elf.o
obj-$(CONFIG_COMPAT_BINFMT_ELF) += compat_binfmt_elf.o
obj-$(CONFIG_BINFMT_ELF_FDPIC) += binfmt_elf_fdpic.o
obj-$(CONFIG_BINFMT_FLAT) += binfmt_flat.o
+obj-$(CONFIG_ARCH_USE_GNU_PROPERTY) += gnu_property.o

obj-$(CONFIG_FS_MBCACHE) += mbcache.o
obj-$(CONFIG_FS_POSIX_ACL) += posix_acl.o
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index fa9e99a..18015fc 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1080,6 +1080,19 @@ static int load_elf_binary(struct linux_binprm *bprm)
}

if (interpreter) {
+ retval = arch_setup_property(&loc->interp_elf_ex,
+ interp_elf_phdata,
+ interpreter, true);
+ } else {
+ retval = arch_setup_property(&loc->elf_ex,
+ elf_phdata,
+ bprm->file, false);
+ }
+
+ if (retval < 0)
+ goto out_free_dentry;
+
+ if (interpreter) {
unsigned long interp_map_addr = 0;

elf_entry = load_elf_interp(&loc->interp_elf_ex,
diff --git a/fs/gnu_property.c b/fs/gnu_property.c
new file mode 100644
index 0000000..656ea39
--- /dev/null
+++ b/fs/gnu_property.c
@@ -0,0 +1,363 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Extract an ELF file's .note.gnu.property.
+ *
+ * The path from the ELF header to the note section is the following:
+ * elfhdr->elf_phdr->elf_note->property[].
+ */
+
+#include <uapi/linux/elf-em.h>
+#include <linux/processor.h>
+#include <linux/binfmts.h>
+#include <linux/elf.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/uaccess.h>
+#include <linux/string.h>
+#include <linux/compat.h>
+
+/*
+ * The .note.gnu.property layout:
+ *
+ * struct elf_note {
+ * u32 n_namesz; --> sizeof(n_name[]); always (4)
+ * u32 n_ndescsz;--> sizeof(property[])
+ * u32 n_type; --> always NT_GNU_PROPERTY_TYPE_0
+ * };
+ * char n_name[4]; --> always 'GNU\0'
+ *
+ * struct {
+ * struct gnu_property {
+ * u32 pr_type;
+ * u32 pr_datasz;
+ * };
+ * u8 pr_data[pr_datasz];
+ * }[];
+ */
+
+#define BUF_SIZE (PAGE_SIZE / 4)
+
+struct gnu_property {
+ u32 pr_type;
+ u32 pr_datasz;
+};
+
+typedef bool (test_item_fn)(void *buf, u32 *arg, u32 type);
+typedef void *(next_item_fn)(void *buf, u32 *arg, u32 type);
+
+static inline bool test_note_type(void *buf, u32 *align, u32 note_type)
+{
+ struct elf_note *n = buf;
+
+ return ((n->n_type == note_type) && (n->n_namesz == 4) &&
+ (memcmp(n + 1, "GNU", 4) == 0));
+}
+
+static inline void *next_note(void *buf, u32 *align, u32 note_type)
+{
+ struct elf_note *n = buf;
+ u64 size;
+
+ if (check_add_overflow((u64)sizeof(*n), (u64)n->n_namesz, &size))
+ return NULL;
+
+ size = round_up(size, *align);
+
+ if (check_add_overflow(size, (u64)n->n_descsz, &size))
+ return NULL;
+
+ size = round_up(size, *align);
+
+ if (buf + size < buf)
+ return NULL;
+ else
+ return (buf + size);
+}
+
+static inline bool test_property(void *buf, u32 *max_type, u32 pr_type)
+{
+ struct gnu_property *pr = buf;
+
+ /*
+ * Property types must be in ascending order.
+ * Keep track of the max when testing each.
+ */
+ if (pr->pr_type > *max_type)
+ *max_type = pr->pr_type;
+
+ return (pr->pr_type == pr_type);
+}
+
+static inline void *next_property(void *buf, u32 *max_type, u32 pr_type)
+{
+ struct gnu_property *pr = buf;
+
+ if ((buf + sizeof(*pr) + pr->pr_datasz < buf) ||
+ (pr->pr_type > pr_type) ||
+ (pr->pr_type > *max_type))
+ return NULL;
+ else
+ return (buf + sizeof(*pr) + pr->pr_datasz);
+}
+
+/*
+ * Scan 'buf' for a pattern; return true if found.
+ * *pos is the distance from the beginning of buf to where
+ * the searched item or the next item is located.
+ */
+static int scan(u8 *buf, u32 buf_size, int item_size, test_item_fn test_item,
+ next_item_fn next_item, u32 *arg, u32 type, u32 *pos)
+{
+ int found = 0;
+ u8 *p, *max;
+
+ max = buf + buf_size;
+ if (max < buf)
+ return 0;
+
+ p = buf;
+
+ while ((p + item_size < max) && (p + item_size > buf)) {
+ if (test_item(p, arg, type)) {
+ found = 1;
+ break;
+ }
+
+ p = next_item(p, arg, type);
+ }
+
+ *pos = (p + item_size <= buf) ? 0 : (u32)(p - buf);
+ return found;
+}
+
+/*
+ * Search an NT_GNU_PROPERTY_TYPE_0 for the property of 'pr_type'.
+ */
+static int find_property(struct file *file, unsigned long desc_size,
+ loff_t file_offset, u8 *buf,
+ u32 pr_type, u32 *property)
+{
+ u32 buf_pos;
+ unsigned long read_size;
+ unsigned long done;
+ int found = 0;
+ int ret = 0;
+ u32 last_pr = 0;
+
+ *property = 0;
+ buf_pos = 0;
+
+ for (done = 0; done < desc_size; done += buf_pos) {
+ read_size = desc_size - done;
+ if (read_size > BUF_SIZE)
+ read_size = BUF_SIZE;
+
+ ret = kernel_read(file, buf, read_size, &file_offset);
+
+ if (ret != read_size)
+ return (ret < 0) ? ret : -EIO;
+
+ ret = 0;
+ found = scan(buf, read_size, sizeof(struct gnu_property),
+ test_property, next_property,
+ &last_pr, pr_type, &buf_pos);
+
+ if ((!buf_pos) || found)
+ break;
+
+ file_offset += buf_pos - read_size;
+ }
+
+ if (found) {
+ struct gnu_property *pr =
+ (struct gnu_property *)(buf + buf_pos);
+
+ if (pr->pr_datasz == 4) {
+ u32 *max = (u32 *)(buf + read_size);
+ u32 *data = (u32 *)((u8 *)pr + sizeof(*pr));
+
+ if (data + 1 <= max) {
+ *property = *data;
+ } else {
+ file_offset += buf_pos - read_size;
+ file_offset += sizeof(*pr);
+ ret = kernel_read(file, property, 4,
+ &file_offset);
+ }
+ }
+ }
+
+ return ret;
+}
+
+/*
+ * Search a PT_NOTE segment for NT_GNU_PROPERTY_TYPE_0.
+ */
+static int find_note_type_0(struct file *file, loff_t file_offset,
+ unsigned long note_size, u32 align,
+ u32 pr_type, u32 *property)
+{
+ u8 *buf;
+ u32 buf_pos;
+ unsigned long read_size;
+ unsigned long done;
+ int found = 0;
+ int ret = 0;
+
+ buf = kmalloc(BUF_SIZE, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ *property = 0;
+ buf_pos = 0;
+
+ for (done = 0; done < note_size; done += buf_pos) {
+ read_size = note_size - done;
+ if (read_size > BUF_SIZE)
+ read_size = BUF_SIZE;
+
+ ret = kernel_read(file, buf, read_size, &file_offset);
+
+ if (ret != read_size) {
+ ret = (ret < 0) ? ret : -EIO;
+ kfree(buf);
+ return ret;
+ }
+
+ /*
+ * item_size = sizeof(struct elf_note) + elf_note.n_namesz.
+ * n_namesz is 4 for the note type we look for.
+ */
+ ret = scan(buf, read_size, sizeof(struct elf_note) + 4,
+ test_note_type, next_note,
+ &align, NT_GNU_PROPERTY_TYPE_0, &buf_pos);
+
+ file_offset += buf_pos - read_size;
+
+ if (ret && !found) {
+ struct elf_note *n =
+ (struct elf_note *)(buf + buf_pos);
+ u64 start = round_up(sizeof(*n) + n->n_namesz, align);
+ u64 total = 0;
+
+ if (check_add_overflow(start, (u64)n->n_descsz, &total)) {
+ ret = -EINVAL;
+ break;
+ }
+ total = round_up(total, align);
+
+ ret = find_property(file, n->n_descsz,
+ file_offset + start,
+ buf, pr_type, property);
+ found++;
+ file_offset += total;
+ buf_pos += total;
+ } else if (!buf_pos || ret) {
+ ret = 0;
+ *property = 0;
+ break;
+ }
+ }
+
+ kfree(buf);
+ return ret;
+}
+
+/*
+ * Look at an ELF file's PT_NOTE segments, then NT_GNU_PROPERTY_TYPE_0, then
+ * the property of pr_type.
+ *
+ * Input:
+ * file: the file to search;
+ * phdr: the file's elf header;
+ * phnum: number of entries in phdr;
+ * pr_type: the property type.
+ *
+ * Output:
+ * The property found.
+ *
+ * Return:
+ * Zero or error.
+ */
+static int scan_segments_64(struct file *file, struct elf64_phdr *phdr,
+ int phnum, u32 pr_type, u32 *property)
+{
+ int i;
+ int err = 0;
+
+ for (i = 0; i < phnum; i++, phdr++) {
+ if ((phdr->p_type != PT_NOTE) || (phdr->p_align != 8))
+ continue;
+
+ /*
+ * Search the PT_NOTE segment for NT_GNU_PROPERTY_TYPE_0.
+ */
+ err = find_note_type_0(file, phdr->p_offset, phdr->p_filesz,
+ phdr->p_align, pr_type, property);
+ if (err)
+ return err;
+ }
+
+ return 0;
+}
+
+#ifdef CONFIG_COMPAT
+static int scan_segments_32(struct file *file, struct elf32_phdr *phdr,
+ int phnum, u32 pr_type, u32 *property)
+{
+ int i;
+ int err = 0;
+
+ for (i = 0; i < phnum; i++, phdr++) {
+ if ((phdr->p_type != PT_NOTE) || (phdr->p_align != 4))
+ continue;
+
+ /*
+ * Search the PT_NOTE segment for NT_GNU_PROPERTY_TYPE_0.
+ */
+ err = find_note_type_0(file, phdr->p_offset, phdr->p_filesz,
+ phdr->p_align, pr_type, property);
+ if (err)
+ return err;
+ }
+
+ return 0;
+}
+#endif
+
+int get_gnu_property(void *ehdr_p, void *phdr_p, struct file *f,
+ u32 pr_type, u32 *property)
+{
+ struct elf64_hdr *ehdr64 = ehdr_p;
+ int err = 0;
+
+ *property = 0;
+
+ if (ehdr64->e_ident[EI_CLASS] == ELFCLASS64) {
+ struct elf64_phdr *phdr64 = phdr_p;
+
+ err = scan_segments_64(f, phdr64, ehdr64->e_phnum,
+ pr_type, property);
+ if (err < 0)
+ goto out;
+ } else {
+#ifdef CONFIG_COMPAT
+ struct elf32_hdr *ehdr32 = ehdr_p;
+
+ if (ehdr32->e_ident[EI_CLASS] == ELFCLASS32) {
+ struct elf32_phdr *phdr32 = phdr_p;
+
+ err = scan_segments_32(f, phdr32, ehdr32->e_phnum,
+ pr_type, property);
+ if (err < 0)
+ goto out;
+ }
+#else
+ WARN_ONCE(1, "Exec of 32-bit app, but CONFIG_COMPAT is not enabled.\n");
+ return -ENOTSUPP;
+#endif
+ }
+
+out:
+ return err;
+}
diff --git a/include/linux/elf.h b/include/linux/elf.h
index e3649b3..c15febe 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -56,4 +56,16 @@ static inline int elf_coredump_extra_notes_write(struct coredump_params *cprm) {
extern int elf_coredump_extra_notes_size(void);
extern int elf_coredump_extra_notes_write(struct coredump_params *cprm);
#endif
+
+#ifdef CONFIG_ARCH_USE_GNU_PROPERTY
+extern int arch_setup_property(void *ehdr, void *phdr, struct file *f,
+ bool interp);
+extern int get_gnu_property(void *ehdr_p, void *phdr_p, struct file *f,
+ u32 pr_type, u32 *feature);
+#else
+static inline int arch_setup_property(void *ehdr, void *phdr, struct file *f,
+ bool interp) { return 0; }
+static inline int get_gnu_property(void *ehdr_p, void *phdr_p, struct file *f,
+ u32 pr_type, u32 *feature) { return 0; }
+#endif
#endif /* _LINUX_ELF_H */
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index 34c02e4..7b7603a 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -372,6 +372,7 @@ typedef struct elf64_shdr {
#define NT_PRFPREG 2
#define NT_PRPSINFO 3
#define NT_TASKSTRUCT 4
+#define NT_GNU_PROPERTY_TYPE_0 5
#define NT_AUXV 6
/*
* Note to userspace developers: size of NT_SIGINFO note may increase
@@ -443,4 +444,11 @@ typedef struct elf64_note {
Elf64_Word n_type; /* Content type */
} Elf64_Nhdr;

+/* .note.gnu.property types */
+#define GNU_PROPERTY_X86_FEATURE_1_AND (0xc0000002)
+
+/* Bits of GNU_PROPERTY_X86_FEATURE_1_AND */
+#define GNU_PROPERTY_X86_FEATURE_1_IBT (0x00000001)
+#define GNU_PROPERTY_X86_FEATURE_1_SHSTK (0x00000002)
+
#endif /* _UAPI_LINUX_ELF_H */
--
2.1.4

Next message: Dave Martin: "[PATCH 2/8] mm: Reserve asm-generic prot flag 0x10 for arch use"
Previous message: Enric Balletbo i Serra: "Re: [PATCH v4 3/3] platform/chrome: cros_ec_spi: Request the SPI thread be realtime"
In reply to: Dave Martin: "[PATCH 0/8] arm64: ARMv8.5-A: Branch Target Identification support"
Next in thread: Dave Martin: "[PATCH 2/8] mm: Reserve asm-generic prot flag 0x10 for arch use"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]