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Subject[PATCH 05/10] x86/cet: ELF header parsing of Control Flow Enforcement
Date
Look in .note.gnu.property of an ELF file and check if shadow stack needs
to be enabled for the task.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
arch/x86/Kconfig | 4 +
arch/x86/include/asm/elf.h | 5 +
arch/x86/include/uapi/asm/elf_property.h | 16 +++
arch/x86/kernel/Makefile | 2 +
arch/x86/kernel/elf.c | 220 +++++++++++++++++++++++++++++++
fs/binfmt_elf.c | 16 +++
include/uapi/linux/elf.h | 1 +
7 files changed, 264 insertions(+)
create mode 100644 arch/x86/include/uapi/asm/elf_property.h
create mode 100644 arch/x86/kernel/elf.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index dd580d4910fc..24339a5299da 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1931,12 +1931,16 @@ config X86_INTEL_CET
config ARCH_HAS_SHSTK
def_bool n

+config ARCH_HAS_PROGRAM_PROPERTIES
+ def_bool n
+
config X86_INTEL_SHADOW_STACK_USER
prompt "Intel Shadow Stack for user-mode"
def_bool n
depends on CPU_SUP_INTEL && X86_64
select X86_INTEL_CET
select ARCH_HAS_SHSTK
+ select ARCH_HAS_PROGRAM_PROPERTIES
---help---
Shadow stack provides hardware protection against program stack
corruption. Only when all the following are true will an application
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 0d157d2a1e2a..5b5f169c5c07 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -382,4 +382,9 @@ struct va_alignment {

extern struct va_alignment va_align;
extern unsigned long align_vdso_addr(unsigned long);
+
+#ifdef CONFIG_ARCH_HAS_PROGRAM_PROPERTIES
+extern int arch_setup_features(void *ehdr, void *phdr, struct file *file,
+ bool interp);
+#endif
#endif /* _ASM_X86_ELF_H */
diff --git a/arch/x86/include/uapi/asm/elf_property.h b/arch/x86/include/uapi/asm/elf_property.h
new file mode 100644
index 000000000000..343a871b8fc1
--- /dev/null
+++ b/arch/x86/include/uapi/asm/elf_property.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _UAPI_ASM_X86_ELF_PROPERTY_H
+#define _UAPI_ASM_X86_ELF_PROPERTY_H
+
+/*
+ * pr_type
+ */
+#define GNU_PROPERTY_X86_FEATURE_1_AND (0xc0000002)
+
+/*
+ * Bits for GNU_PROPERTY_X86_FEATURE_1_AND
+ */
+#define GNU_PROPERTY_X86_FEATURE_1_SHSTK (0x00000002)
+#define GNU_PROPERTY_X86_FEATURE_1_IBT (0x00000001)
+
+#endif /* _UAPI_ASM_X86_ELF_PROPERTY_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 7ea5e099d558..cbf983f44b61 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -140,6 +140,8 @@ obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o

obj-$(CONFIG_X86_INTEL_CET) += cet.o

+obj-$(CONFIG_ARCH_HAS_PROGRAM_PROPERTIES) += elf.o
+
###
# 64 bit specific files
ifeq ($(CONFIG_X86_64),y)
diff --git a/arch/x86/kernel/elf.c b/arch/x86/kernel/elf.c
new file mode 100644
index 000000000000..8e2719d8dc86
--- /dev/null
+++ b/arch/x86/kernel/elf.c
@@ -0,0 +1,220 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Look at an ELF file's .note.gnu.property and determine if the file
+ * supports shadow stack and/or indirect branch tracking.
+ * The path from the ELF header to the note section is the following:
+ * elfhdr->elf_phdr->elf_note->x86_note_gnu_property[].
+ */
+
+#include <asm/cet.h>
+#include <asm/elf_property.h>
+#include <uapi/linux/elf-em.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>
+
+#define ELF_NOTE_DESC_OFFSET(n, align) \
+ round_up(sizeof(*n) + n->n_namesz, (align))
+
+#define ELF_NOTE_NEXT_OFFSET(n, align) \
+ round_up(ELF_NOTE_DESC_OFFSET(n, align) + n->n_descsz, (align))
+
+static int find_cet(u8 *buf, u32 size, u32 align, int *shstk, int *ibt)
+{
+ unsigned long start = (unsigned long)buf;
+ struct elf_note *note = (struct elf_note *)buf;
+
+ *shstk = 0;
+ *ibt = 0;
+
+ /*
+ * Go through the x86_note_gnu_property array pointed by
+ * buf and look for shadow stack and indirect branch
+ * tracking features.
+ * The GNU_PROPERTY_X86_FEATURE_1_AND entry contains only
+ * one u32 as data. Do not go beyond buf_size.
+ */
+
+ while ((unsigned long) (note + 1) - start < size) {
+ /* Find the NT_GNU_PROPERTY_TYPE_0 note. */
+ if (note->n_namesz == 4 &&
+ note->n_type == NT_GNU_PROPERTY_TYPE_0 &&
+ memcmp(note + 1, "GNU", 4) == 0) {
+ u8 *ptr, *ptr_end;
+
+ /* Check for invalid property. */
+ if (note->n_descsz < 8 ||
+ (note->n_descsz % align) != 0)
+ return 0;
+
+ /* Start and end of property array. */
+ ptr = (u8 *)(note + 1) + 4;
+ ptr_end = ptr + note->n_descsz;
+
+ while (1) {
+ u32 type = *(u32 *)ptr;
+ u32 datasz = *(u32 *)(ptr + 4);
+
+ ptr += 8;
+ if ((ptr + datasz) > ptr_end)
+ break;
+
+ if (type == GNU_PROPERTY_X86_FEATURE_1_AND &&
+ datasz == 4) {
+ u32 p = *(u32 *)ptr;
+
+ if (p & GNU_PROPERTY_X86_FEATURE_1_SHSTK)
+ *shstk = 1;
+ if (p & GNU_PROPERTY_X86_FEATURE_1_IBT)
+ *ibt = 1;
+ return 1;
+ }
+ }
+ }
+
+ /*
+ * Note sections like .note.ABI-tag and .note.gnu.build-id
+ * are aligned to 4 bytes in 64-bit ELF objects.
+ */
+ note = (void *)note + ELF_NOTE_NEXT_OFFSET(note, align);
+ }
+
+ return 0;
+}
+
+static int check_pt_note_segment(struct file *file,
+ unsigned long note_size, loff_t *pos,
+ u32 align, int *shstk, int *ibt)
+{
+ int retval;
+ char *note_buf;
+
+ /*
+ * Try to read in the whole PT_NOTE segment.
+ */
+ note_buf = kmalloc(note_size, GFP_KERNEL);
+ if (!note_buf)
+ return -ENOMEM;
+ retval = kernel_read(file, note_buf, note_size, pos);
+ if (retval != note_size) {
+ kfree(note_buf);
+ return (retval < 0) ? retval : -EIO;
+ }
+
+ retval = find_cet(note_buf, note_size, align, shstk, ibt);
+ kfree(note_buf);
+ return retval;
+}
+
+#ifdef CONFIG_COMPAT
+static int check_pt_note_32(struct file *file, struct elf32_phdr *phdr,
+ int phnum, int *shstk, int *ibt)
+{
+ int i;
+ int found = 0;
+
+ /*
+ * Go through all PT_NOTE segments and find NT_GNU_PROPERTY_TYPE_0.
+ */
+ for (i = 0; i < phnum; i++, phdr++) {
+ loff_t pos;
+
+ /*
+ * NT_GNU_PROPERTY_TYPE_0 note is aligned to 4 bytes
+ * in 32-bit binaries.
+ */
+ if ((phdr->p_type != PT_NOTE) || (phdr->p_align != 4))
+ continue;
+
+ pos = phdr->p_offset;
+ found = check_pt_note_segment(file, phdr->p_filesz,
+ &pos, phdr->p_align,
+ shstk, ibt);
+ if (found)
+ break;
+ }
+ return found;
+}
+#endif
+
+#ifdef CONFIG_X86_64
+static int check_pt_note_64(struct file *file, struct elf64_phdr *phdr,
+ int phnum, int *shstk, int *ibt)
+{
+ int found = 0;
+
+ /*
+ * Go through all PT_NOTE segments and find NT_GNU_PROPERTY_TYPE_0.
+ */
+ for (; phnum > 0; phnum--, phdr++) {
+ loff_t pos;
+
+ /*
+ * NT_GNU_PROPERTY_TYPE_0 note is aligned to 8 bytes
+ * in 64-bit binaries.
+ */
+ if ((phdr->p_type != PT_NOTE) || (phdr->p_align != 8))
+ continue;
+
+ pos = phdr->p_offset;
+ found = check_pt_note_segment(file, phdr->p_filesz,
+ &pos, phdr->p_align,
+ shstk, ibt);
+
+ if (found)
+ break;
+ }
+ return found;
+}
+#endif
+
+int arch_setup_features(void *ehdr_p, void *phdr_p,
+ struct file *file, bool interp)
+{
+ int err = 0;
+ int shstk = 0;
+ int ibt = 0;
+
+ struct elf64_hdr *ehdr64 = ehdr_p;
+
+ if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
+ return 0;
+
+ if (ehdr64->e_ident[EI_CLASS] == ELFCLASS64) {
+ struct elf64_phdr *phdr64 = phdr_p;
+
+ err = check_pt_note_64(file, phdr64, ehdr64->e_phnum,
+ &shstk, &ibt);
+ 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 = check_pt_note_32(file, phdr32, ehdr32->e_phnum,
+ &shstk, &ibt);
+ if (err < 0)
+ goto out;
+ }
+#endif
+ }
+
+ current->thread.cet.shstk_enabled = 0;
+ current->thread.cet.shstk_base = 0;
+ current->thread.cet.shstk_size = 0;
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+ if (shstk) {
+ err = cet_setup_shstk();
+ if (err < 0)
+ goto out;
+ }
+ }
+out:
+ return err;
+}
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 4ad6f669fe34..9ddc6d01e779 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1081,6 +1081,22 @@ static int load_elf_binary(struct linux_binprm *bprm)
goto out_free_dentry;
}

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

diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index e2535d6dcec7..f69ed8702271 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
--
2.15.1
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