[RFC PATCH v9 24/27] x86/cet/shstk: ELF header parsing for Shadow Stack

Yu-cheng Yu
2020-02-05T18:20:56Z

Check an ELF file's .note.gnu.property, and setup Shadow Stack if the
application supports it.

v9:
- Change cpu_feature_enabled() to static_cpu_has().

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
arch/x86/Kconfig | 2 ++
arch/x86/include/asm/elf.h | 13 +++++++++++++
arch/x86/kernel/process_64.c | 31 +++++++++++++++++++++++++++++++
3 files changed, 46 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6c34b701c588..d1447380e02e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1987,6 +1987,8 @@ config X86_INTEL_SHADOW_STACK_USER
select ARCH_USES_HIGH_VMA_FLAGS
select X86_INTEL_CET
select ARCH_HAS_SHSTK
+ select ARCH_USE_GNU_PROPERTY
+ select ARCH_BINFMT_ELF_STATE
---help---
Shadow Stack (SHSTK) provides protection against program
stack corruption. It is active when the kernel has this
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 69c0f892e310..fac79b621e0a 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -367,6 +367,19 @@ extern int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
int uses_interp);
#define compat_arch_setup_additional_pages compat_arch_setup_additional_pages

+#ifdef CONFIG_ARCH_BINFMT_ELF_STATE
+struct arch_elf_state {
+ unsigned int gnu_property;
+};
+
+#define INIT_ARCH_ELF_STATE { \
+ .gnu_property = 0, \
+}
+
+#define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) (0)
+#define arch_check_elf(ehdr, interp, interp_ehdr, state) (0)
+#endif
+
/* Do not change the values. See get_align_mask() */
enum align_flags {
ALIGN_VA_32 = BIT(0),
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 506d66830d4d..99548cde0cc6 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -732,3 +732,34 @@ unsigned long KSTK_ESP(struct task_struct *task)
{
return task_pt_regs(task)->sp;
}
+
+#ifdef CONFIG_ARCH_USE_GNU_PROPERTY
+int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
+ bool compat, struct arch_elf_state *state)
+{
+ if (type != GNU_PROPERTY_X86_FEATURE_1_AND)
+ return 0;
+
+ if (datasz != sizeof(unsigned int))
+ return -ENOEXEC;
+
+ state->gnu_property = *(unsigned int *)data;
+ return 0;
+}
+
+int arch_setup_elf_property(struct arch_elf_state *state)
+{
+ int r = 0;
+
+ memset(&current->thread.cet, 0, sizeof(struct cet_status));
+
+ if (static_cpu_has(X86_FEATURE_SHSTK)) {
+ if (state->gnu_property & GNU_PROPERTY_X86_FEATURE_1_SHSTK)
+ r = cet_setup_shstk();
+ if (r < 0)
+ return r;
+ }
+
+ return r;
+}
+#endif
--
2.21.0