This patch was part of the Intel Control-flow Enforcement (CET) series at:
https://lkml.org/lkml/2019/6/6/1014.
In the discussion, we decided to look at only an ELF header's
PT_GNU_PROPERTY, which is a shortcut pointing to the file's
.note.gnu.property.
The Linux gABI extension draft is here:
https://github.com/hjl-tools/linux-abi/wiki/linux-abi-draft.pdf.
A few existing CET-enabled binary files were built without
PT_GNU_PROPERTY; but those files' .note.gnu.property are checked by
ld-linux, not Linux. The compatibility impact from this change is
therefore managable.
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().
This work is derived from code provided by H.J. Lu <hjl.tools@xxxxxxxxx>.
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
fs/Kconfig.binfmt | 3 +
fs/Makefile | 1 +
fs/binfmt_elf.c | 20 +++
fs/gnu_property.c | 279 +++++++++++++++++++++++++++++++++++++++
include/linux/elf.h | 11 ++
include/uapi/linux/elf.h | 14 ++
6 files changed, 328 insertions(+)
create mode 100644 fs/gnu_property.c
diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index f87ddd1b6d72..397138ab305b 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 c9aea23aba56..b69f18c14e09 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 8264b468f283..cbc6d68f4a18 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..37cd503a0c48
--- /dev/null
+++ b/fs/gnu_property.c
@@ -0,0 +1,279 @@
+/* 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 (5)
+ * };
+ * char n_name[4]; --> always 'GNU\0'
+ *
+ * struct {
+ * struct gnu_property {
+ * u32 pr_type;
+ * u32 pr_datasz;
+ * };
+ * u8 pr_data[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 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 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(u32 pr_type, u32 *property, struct file *file,
+ loff_t file_offset, unsigned long desc_size)
+{
+ u8 *buf;
+ int buf_size;
+
+ 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;
+
+ buf_size = (desc_size > PAGE_SIZE) ? PAGE_SIZE : desc_size;
+ buf = kmalloc(buf_size, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ 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);
+ }
+ }
+ }
+
+ kfree(buf);
+ return ret;
+}
+
+/*
+ * Look at an ELF file's PT_GNU_PROPERTY for 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, err;
+
+ err = 0;
+
+ for (i = 0; i < phnum; i++, phdr++) {
+ if (phdr->p_align != 8)
+ continue;
+
+ if (phdr->p_type == PT_GNU_PROPERTY) {
+ struct elf64_note n;
+ loff_t pos;
+
+ /* read note header */
+ pos = phdr->p_offset;
+ err = kernel_read(file, &n, sizeof(n), &pos);
+ if (err < sizeof(n))
+ return -EIO;
+
+ /* find note payload offset */
+ pos = phdr->p_offset + round_up(sizeof(n) + n.n_namesz,
+ phdr->p_align);
+
+ err = find_property(pr_type, property, file,
+ pos, n.n_descsz);
+ break;
+ }
+ }
+
+ return err;
+}
+
+static int scan_segments_32(struct file *file, struct elf32_phdr *phdr,
+ int phnum, u32 pr_type, u32 *property)
+{
+ int i, err;
+
+ err = 0;
+
+ for (i = 0; i < phnum; i++, phdr++) {
+ if (phdr->p_align != 4)
+ continue;
+
+ if (phdr->p_type == PT_GNU_PROPERTY) {
+ struct elf32_note n;
+ loff_t pos;
+
+ /* read note header */
+ pos = phdr->p_offset;
+ err = kernel_read(file, &n, sizeof(n), &pos);
+ if (err < sizeof(n))
+ return -EIO;
+
+ /* find note payload offset */
+ pos = phdr->p_offset + round_up(sizeof(n) + n.n_namesz,
+ phdr->p_align);
+
+ err = find_property(pr_type, property, file,
+ pos, n.n_descsz);
+ break;
+ }
+ }
+
+ return err;
+}
+
+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 {
+ 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;
+ }
+ }
+
+out:
+ 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
