[PATCH v15 23/26] ELF: Introduce arch_setup_elf_property()

Yu-cheng Yu
2020-11-10T16:23:01Z

An ELF file's .note.gnu.property indicates arch features supported by the
file. These features are extracted by arch_parse_elf_property() and stored
in 'arch_elf_state'. Introduce arch_setup_elf_property() for enabling such
features. The first use-case of this function is shadow stack.

ARM64 is the other arch that has ARCH_USER_GNU_PROPERTY and arch_parse_elf_
property(). Add arch_setup_elf_property() for it.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Martin <Dave.Martin@arm.com>
---
arch/arm64/include/asm/elf.h | 5 +++++
arch/x86/Kconfig | 2 ++
arch/x86/include/asm/elf.h | 13 +++++++++++++
arch/x86/kernel/process_64.c | 32 ++++++++++++++++++++++++++++++++
fs/binfmt_elf.c | 4 ++++
include/linux/elf.h | 6 ++++++
6 files changed, 62 insertions(+)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 8d1c8dcb87fd..d37bc7915935 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -281,6 +281,11 @@ static inline int arch_parse_elf_property(u32 type, const void *data,
return 0;
}

+static inline int arch_setup_elf_property(struct arch_elf_state *arch)
+{
+ return 0;
+}
+
static inline int arch_elf_pt_proc(void *ehdr, void *phdr,
struct file *f, bool is_interp,
struct arch_elf_state *state)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 960993862b96..18fd8cb549ad 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1953,6 +1953,8 @@ config X86_SHADOW_STACK_USER
select X86_CET
select ARCH_MAYBE_MKWRITE
select ARCH_HAS_SHADOW_STACK
+ select ARCH_USE_GNU_PROPERTY
+ select ARCH_BINFMT_ELF_STATE
help
Shadow Stacks provides protection against program stack
corruption. It's a hardware feature. This only matters
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index b9a5d488f1a5..0e1be2a13359 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -385,6 +385,19 @@ 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 df342bedea88..7c4687a0f001 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -837,3 +837,35 @@ 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;
+
+ if (!IS_ENABLED(CONFIG_X86_CET))
+ return r;
+
+ 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();
+ }
+
+ return r;
+}
+#endif
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index fa50e8936f5f..1ae32cc0f61b 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1245,6 +1245,10 @@ static int load_elf_binary(struct linux_binprm *bprm)

set_binfmt(&elf_format);

+ retval = arch_setup_elf_property(&arch_state);
+ if (retval < 0)
+ goto out;
+
#ifdef ARCH_HAS_SETUP_ADDITIONAL_PAGES
retval = arch_setup_additional_pages(bprm, !!interpreter);
if (retval < 0)
diff --git a/include/linux/elf.h b/include/linux/elf.h
index 5d5b0321da0b..4827695ca415 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -82,9 +82,15 @@ static inline int arch_parse_elf_property(u32 type, const void *data,
{
return 0;
}
+
+static inline int arch_setup_elf_property(struct arch_elf_state *arch)
+{
+ return 0;
+}
#else
extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
bool compat, struct arch_elf_state *arch);
+extern int arch_setup_elf_property(struct arch_elf_state *arch);
#endif

#ifdef CONFIG_ARCH_HAVE_ELF_PROT
--
2.21.0