[PATCH v8 22/27] binfmt_elf: Extract .note.gnu.property from an ELF file

Yu-cheng Yu
2019-08-13T21:03:05Z

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.

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

This patch is derived from code provided by H.J. Lu <hjl.tools@gmail.com>.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
fs/Kconfig.binfmt | 3 +
fs/Makefile | 1 +
fs/binfmt_elf.c | 20 +++++
fs/gnu_property.c | 178 +++++++++++++++++++++++++++++++++++++++
include/linux/elf.h | 11 +++
include/uapi/linux/elf.h | 14 +++
6 files changed, 227 insertions(+)
create mode 100644 fs/gnu_property.c

diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index 62dc4f577ba1..d2cfe0729a73 100644
--- a/fs/Kconfig.binfmt
+++ b/fs/Kconfig.binfmt
@@ -36,6 +36,9 @@ config COMPAT_BINFMT_ELF
config ARCH_BINFMT_ELF_STATE
bool

+config ARCH_USE_GNU_PROPERTY
+ bool
+
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 d60089fd689b..939b1eb7e8cc 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 d4e11b2e04f6..a4e87fcb10a8 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -852,6 +852,21 @@ static int load_elf_binary(struct linux_binprm *bprm)
}
}

+ if (interpreter) {
+ retval = arch_parse_property(&loc->interp_elf_ex,
+ interp_elf_phdata,
+ interpreter, true,
+ &arch_state);
+ } else {
+ retval = arch_parse_property(&loc->elf_ex,
+ elf_phdata,
+ bprm->file, false,
+ &arch_state);
+ }
+
+ if (retval)
+ goto out_free_dentry;
+
/*
* Allow arch code to reject the ELF at this point, whilst it's
* still possible to return an error to the code that invoked
@@ -1080,6 +1095,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
goto out_free_dentry;
}

+ retval = arch_setup_property(&arch_state);
+
+ if (retval < 0)
+ goto out_free_dentry;
+
if (interpreter) {
unsigned long interp_map_addr = 0;

diff --git a/fs/gnu_property.c b/fs/gnu_property.c
new file mode 100644
index 000000000000..b22b43f4d6a0
--- /dev/null
+++ b/fs/gnu_property.c
@@ -0,0 +1,178 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Extract an ELF file's .note.gnu.property.
+ *
+ * The path from the ELF header to .note.gnu.property is:
+ * elfhdr->elf_phdr->elf_note.
+ *
+ * .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 (5)
+ * };
+ * char n_name[4]; --> always 'GNU\0'
+ *
+ * struct {
+ * struct gnu_property {
+ * u32 pr_type;
+ * u32 pr_datasz;
+ * };
+ * u8 pr_data[pr_datasz];
+ * }[];
+ */
+
+#include <linux/elf.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/string.h>
+#include <linux/compat.h>
+
+/*
+ * Search a note's payload for 'pr_type'.
+ */
+static int check_note_payload(void *buf, unsigned long len, u32 pr_type,
+ u32 *property)
+{
+ u32 pr_type_max = 0;
+
+ *property = 0;
+
+ while (len > 0) {
+ struct gnu_property *pr = buf;
+ unsigned long pr_len;
+
+ if (sizeof(*pr) > len)
+ return 0;
+
+ pr_len = sizeof(*pr) + pr->pr_datasz;
+
+ if (pr_len > len)
+ return -ENOEXEC;
+
+ /* property types are in ascending order */
+ if ((pr_type_max != 0) && (pr->pr_type > pr_type_max))
+ return 0;
+
+ if (pr->pr_type > pr_type)
+ return 0;
+
+ if ((pr->pr_type == pr_type) &&
+ (pr->pr_datasz >= sizeof(u32))) {
+ *property = *(u32 *)(buf + sizeof(*pr));
+ return 0;
+ }
+
+ if (pr->pr_type > pr_type_max)
+ pr_type_max = pr->pr_type;
+
+ buf += pr_len;
+ len -= pr_len;
+ }
+
+ return 0;
+}
+
+/*
+ * Look at an ELF file's NT_GNU_PROPERTY for the property of pr_type.
+ *
+ * Input:
+ * buf: the buffer containing the whole note.
+ * len: size of buf.
+ * align: alignment of the note's payload.
+ * pr_type: the property type.
+ *
+ * Output:
+ * The property found.
+ *
+ * Return:
+ * Zero or error.
+ */
+static int check_note(void *buf, unsigned long len, int align,
+ u32 pr_type, u32 *property)
+{
+ struct elf_note *n = buf;
+ char *note_name = buf + sizeof(*n);
+ unsigned long payload_offset;
+ unsigned long payload_len;
+
+ if (len < sizeof(*n) + 4)
+ return -ENOEXEC;
+
+ if ((n->n_namesz != 4) || strncmp("GNU", note_name, 3))
+ return -ENOEXEC;
+
+ payload_offset = round_up(sizeof(*n) + n->n_namesz, align);
+ payload_len = n->n_descsz;
+
+ if (payload_offset + payload_len > len)
+ return -ENOEXEC;
+
+ buf += payload_offset;
+ len -= payload_offset;
+
+ return check_note_payload(buf, len, pr_type, property);
+}
+
+#define find_note(phdr, nr_phdrs, align, pos, len) { \
+ int cnt; \
+ \
+ for (cnt = 0; cnt < nr_phdrs; cnt++) { \
+ if ((phdr)[cnt].p_align != align) \
+ continue; \
+ if ((phdr)[cnt].p_type == PT_GNU_PROPERTY) { \
+ pos = (phdr)[cnt].p_offset; \
+ len = (phdr)[cnt].p_filesz; \
+ } \
+ } \
+}
+
+int get_gnu_property(void *ehdr, void *phdr, struct file *file,
+ u32 pr_type, u32 *property)
+{
+ Elf64_Ehdr *ehdr64 = ehdr;
+ Elf32_Ehdr *ehdr32 = ehdr;
+ void *buf;
+ int align;
+ loff_t pos = 0;
+ unsigned long len = 0;
+ int err = 0;
+
+ /*
+ * Find PT_GNU_PROPERTY from ELF program headers.
+ */
+ if (ehdr64->e_ident[EI_CLASS] == ELFCLASS64) {
+ align = 8;
+ find_note((Elf64_Phdr *)phdr, ehdr64->e_phnum, align, pos, len);
+ } else if (ehdr32->e_ident[EI_CLASS] == ELFCLASS32) {
+ align = 4;
+ find_note((Elf32_Phdr *)phdr, ehdr32->e_phnum, align, pos, len);
+ }
+
+ /*
+ * Read in the whole note. PT_GNU_PROPERTY
+ * is not expected to be larger than a page.
+ */
+ if (len == 0)
+ return 0;
+
+ if (len > PAGE_SIZE)
+ return -ENOEXEC;
+
+ buf = kmalloc(len, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ err = kernel_read(file, buf, len, &pos);
+ if (err < len) {
+ if (err >= 0)
+ err = -EIO;
+ goto out;
+ }
+
+ err = check_note(buf, len, align, pr_type, property);
+out:
+ kfree(buf);
+ return err;
+}
diff --git a/include/linux/elf.h b/include/linux/elf.h
index e3649b3e970e..c86cbfd17382 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -56,4 +56,15 @@ 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_parse_property(void *ehdr, void *phdr, struct file *f,
+ bool inter, struct arch_elf_state *state);
+extern int arch_setup_property(struct arch_elf_state *state);
+extern int get_gnu_property(void *ehdr_p, void *phdr_p, struct file *f,
+ u32 pr_type, u32 *feature);
+#else
+#define arch_parse_property(ehdr, phdr, file, inter, state) (0)
+#define arch_setup_property(state) (0)
+#endif
#endif /* _LINUX_ELF_H */
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index 34c02e4290fe..530ce08467c2 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -36,6 +36,7 @@ typedef __s64 Elf64_Sxword;
#define PT_LOPROC 0x70000000
#define PT_HIPROC 0x7fffffff
#define PT_GNU_EH_FRAME 0x6474e550
+#define PT_GNU_PROPERTY 0x6474e553

#define PT_GNU_STACK (PT_LOOS + 0x474e551)

@@ -443,4 +444,17 @@ typedef struct elf64_note {
Elf64_Word n_type; /* Content type */
} Elf64_Nhdr;

+/* NT_GNU_PROPERTY_TYPE_0 header */
+struct gnu_property {
+ __u32 pr_type;
+ __u32 pr_datasz;
+};
+
+/* .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 */
--
2.17.1