From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eugene Syromiatnikov Subject: Re: [RFC PATCH v4 21/27] x86/cet/shstk: ELF header parsing of Shadow Stack Date: Thu, 4 Oct 2018 01:27:36 +0200 Message-ID: <20181003232736.GI32759@asgard.redhat.com> References: <20180921150351.20898-1-yu-cheng.yu@intel.com> <20180921150351.20898-22-yu-cheng.yu@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20180921150351.20898-22-yu-cheng.yu@intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Yu-cheng Yu Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek Peter List-Id: linux-arch.vger.kernel.org On Fri, Sep 21, 2018 at 08:03:45AM -0700, Yu-cheng Yu wrote: > 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 > Signed-off-by: Yu-cheng Yu > --- > arch/x86/Kconfig | 4 + > arch/x86/include/asm/elf.h | 5 + > arch/x86/include/uapi/asm/elf_property.h | 15 + > arch/x86/kernel/Makefile | 2 + > arch/x86/kernel/elf.c | 340 +++++++++++++++++++++++ > fs/binfmt_elf.c | 15 + > include/uapi/linux/elf.h | 1 + > 7 files changed, 382 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 808aa3aecf3c..6377125543cc 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -1919,12 +1919,16 @@ 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..af361207718c > --- /dev/null > +++ b/arch/x86/include/uapi/asm/elf_property.h > @@ -0,0 +1,15 @@ > +/* 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) Hm, these defeinitions aren't much different comparing to NT_* definitions in include/uapi/linux/elf.h, is it expected that those properties have to be parsed individually for each architecture? > + > +#endif /* _UAPI_ASM_X86_ELF_PROPERTY_H */ > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile > index fbb2d91fb756..36b14ef410c8 100644 > --- a/arch/x86/kernel/Makefile > +++ b/arch/x86/kernel/Makefile > @@ -141,6 +141,8 @@ obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o > > obj-$(CONFIG_X86_INTEL_CET) += cet.o > > +obj-$(CONFIG_ARCH_HAS_PROGRAM_PROPERTIES) += elf.o Same thing here, enablement of program properties per se seems rather generic. > diff --git a/arch/x86/kernel/elf.c b/arch/x86/kernel/elf.c > new file mode 100644 > index 000000000000..2fddd0bc545b > --- /dev/null > +++ b/arch/x86/kernel/elf.c > @@ -0,0 +1,340 @@ > +/* 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->property[]. > + */ > + > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > + > +/* > + * 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 > + * }; > + * char n_name[4]; --> always 'GNU\0' > + * > + * struct { > + * struct property_x86 { > + * u32 pr_type; > + * u32 pr_datasz; > + * }; > + * u8 pr_data[pr_datasz]; > + * }[]; > + */ > + > +#define BUF_SIZE (PAGE_SIZE / 4) > + > +struct property_x86 { > + u32 pr_type; > + u32 pr_datasz; > +}; > + > +typedef bool (test_fn)(void *buf, u32 *arg); > +typedef void *(next_fn)(void *buf, u32 *arg); > + > +static inline bool test_note_type_0(void *buf, u32 *arg) > +{ > + struct elf_note *n = buf; > + > + return ((n->n_namesz == 4) && (memcmp(n + 1, "GNU", 4) == 0) && > + (n->n_type == NT_GNU_PROPERTY_TYPE_0)); > +} > + > +static inline void *next_note(void *buf, u32 *arg) > +{ > + struct elf_note *n = buf; > + u32 align = *arg; > + int size; > + > + size = round_up(sizeof(*n) + n->n_namesz, align); > + size = round_up(size + n->n_descsz, align); > + > + if (buf + size < buf) > + return NULL; > + else > + return (buf + size); > +} > + > +static inline bool test_property_x86(void *buf, u32 *arg) > +{ > + struct property_x86 *pr = buf; > + u32 max_type = *arg; > + > + if (pr->pr_type > max_type) > + *arg = pr->pr_type; > + > + return (pr->pr_type == GNU_PROPERTY_X86_FEATURE_1_AND); > +} > + > +static inline void *next_property(void *buf, u32 *arg) > +{ > + struct property_x86 *pr = buf; > + u32 max_type = *arg; > + > + if ((buf + sizeof(*pr) + pr->pr_datasz < buf) || > + (pr->pr_type > GNU_PROPERTY_X86_FEATURE_1_AND) || > + (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_fn test, next_fn next, u32 *arg, 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(p, arg)) { > + found = 1; > + break; > + } > + > + p = next(p, arg); > + } > + > + *pos = (p + item_size <= buf) ? 0 : (u32)(p - buf); > + return found; > +} > + > +/* > + * Search a NT_GNU_PROPERTY_TYPE_0 for GNU_PROPERTY_X86_FEATURE_1_AND. > + */ > +static int find_feature_x86(struct file *file, unsigned long desc_size, > + loff_t file_offset, u8 *buf, u32 *feature) > +{ > + u32 buf_pos; > + unsigned long read_size; > + unsigned long done; > + int found = 0; > + int ret = 0; > + u32 last_pr = 0; > + > + *feature = 0; > + buf_pos = 0; > + > + 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 property_x86), > + test_property_x86, next_property, > + &last_pr, &buf_pos); > + > + if ((!buf_pos) || found) > + break; > + > + file_offset += buf_pos - read_size; > + } > + > + if (found) { > + struct property_x86 *pr = > + (struct property_x86 *)(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) { > + *feature = *data; > + } else { > + file_offset += buf_pos - read_size; > + file_offset += sizeof(*pr); > + ret = kernel_read(file, feature, 4, > + &file_offset); > + } > + } > + } > + > + return ret; > +} > + > +/* > + * Search a PT_NOTE segment for the first NT_GNU_PROPERTY_TYPE_0. > + */ > +static int find_note_type_0(struct file *file, unsigned long note_size, > + loff_t file_offset, u32 align, u32 *feature) > +{ > + u8 *buf; > + u32 buf_pos; > + unsigned long read_size; > + unsigned long done; > + int found = 0; > + int ret = 0; > + > + buf = kmalloc(BUF_SIZE, GFP_KERNEL); > + if (!buf) > + return -ENOMEM; > + > + *feature = 0; > + buf_pos = 0; > + > + for (done = 0; done < note_size; done += buf_pos) { > + read_size = note_size - done; > + if (read_size > BUF_SIZE) > + read_size = BUF_SIZE; > + > + ret = kernel_read(file, buf, read_size, &file_offset); > + > + if (ret != read_size) { > + ret = (ret < 0) ? ret : -EIO; > + kfree(buf); > + return ret; > + } > + > + /* > + * item_size = sizeof(struct elf_note) + elf_note.n_namesz. > + * n_namesz is 4 for the note type we look for. > + */ > + ret = 0; > + found += scan(buf, read_size, sizeof(struct elf_note) + 4, > + test_note_type_0, next_note, > + &align, &buf_pos); > + > + file_offset += buf_pos - read_size; > + > + if (found == 1) { > + struct elf_note *n = > + (struct elf_note *)(buf + buf_pos); > + u32 start = round_up(sizeof(*n) + n->n_namesz, align); > + u32 total = round_up(start + n->n_descsz, align); > + > + ret = find_feature_x86(file, n->n_descsz, > + file_offset + start, > + buf, feature); > + file_offset += total; > + buf_pos += total; > + } else if (!buf_pos) { > + *feature = 0; > + break; > + } > + } > + > + kfree(buf); > + return ret; > +} > + > +#ifdef CONFIG_COMPAT > +static int check_notes_32(struct file *file, struct elf32_phdr *phdr, > + int phnum, u32 *feature) > +{ > + int i; > + int err = 0; > + > + for (i = 0; i < phnum; i++, phdr++) { > + if ((phdr->p_type != PT_NOTE) || (phdr->p_align != 4)) > + continue; > + > + err = find_note_type_0(file, phdr->p_filesz, phdr->p_offset, > + phdr->p_align, feature); > + if (err) > + return err; > + } > + > + return 0; > +} > +#endif > + > +#ifdef CONFIG_X86_64 > +static int check_notes_64(struct file *file, struct elf64_phdr *phdr, > + int phnum, u32 *feature) > +{ > + int i; > + int err = 0; > + > + for (i = 0; i < phnum; i++, phdr++) { > + if ((phdr->p_type != PT_NOTE) || (phdr->p_align != 8)) > + continue; > + > + err = find_note_type_0(file, phdr->p_filesz, phdr->p_offset, > + phdr->p_align, feature); > + if (err) > + return err; > + } > + > + return 0; > +} > +#endif > + > +int arch_setup_features(void *ehdr_p, void *phdr_p, > + struct file *file, bool interp) > +{ > + int err = 0; > + u32 feature = 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_notes_64(file, phdr64, ehdr64->e_phnum, > + &feature); > + 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_notes_32(file, phdr32, ehdr32->e_phnum, > + &feature); > + if (err < 0) > + goto out; > + } > +#endif > + } > + > + memset(¤t->thread.cet, 0, sizeof(struct cet_status)); > + > + if (cpu_feature_enabled(X86_FEATURE_SHSTK)) { > + if (feature & GNU_PROPERTY_X86_FEATURE_1_SHSTK) { > + err = cet_setup_shstk(); > + if (err < 0) > + goto out; > + } > + } > + > +out: > + return err; > +} There's a lot of similar code with bpf stackmap .build-id code (commit v4.17-rc1~148^2~156^2~3^2~1), it might be worthy generalising some ELF traversal routines, since there's general need of parsing ELF property segments. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:20328 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726182AbeJDGRs (ORCPT ); Thu, 4 Oct 2018 02:17:48 -0400 Date: Thu, 4 Oct 2018 01:27:36 +0200 From: Eugene Syromiatnikov Subject: Re: [RFC PATCH v4 21/27] x86/cet/shstk: ELF header parsing of Shadow Stack Message-ID: <20181003232736.GI32759@asgard.redhat.com> References: <20180921150351.20898-1-yu-cheng.yu@intel.com> <20180921150351.20898-22-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180921150351.20898-22-yu-cheng.yu@intel.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Yu-cheng Yu Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue Message-ID: <20181003232736.RtPvaVBCCJ4VZHrJQASyb1t3cjBK1YSad4LQ3PIC9ac@z> On Fri, Sep 21, 2018 at 08:03:45AM -0700, Yu-cheng Yu wrote: > 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 > Signed-off-by: Yu-cheng Yu > --- > arch/x86/Kconfig | 4 + > arch/x86/include/asm/elf.h | 5 + > arch/x86/include/uapi/asm/elf_property.h | 15 + > arch/x86/kernel/Makefile | 2 + > arch/x86/kernel/elf.c | 340 +++++++++++++++++++++++ > fs/binfmt_elf.c | 15 + > include/uapi/linux/elf.h | 1 + > 7 files changed, 382 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 808aa3aecf3c..6377125543cc 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -1919,12 +1919,16 @@ 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..af361207718c > --- /dev/null > +++ b/arch/x86/include/uapi/asm/elf_property.h > @@ -0,0 +1,15 @@ > +/* 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) Hm, these defeinitions aren't much different comparing to NT_* definitions in include/uapi/linux/elf.h, is it expected that those properties have to be parsed individually for each architecture? > + > +#endif /* _UAPI_ASM_X86_ELF_PROPERTY_H */ > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile > index fbb2d91fb756..36b14ef410c8 100644 > --- a/arch/x86/kernel/Makefile > +++ b/arch/x86/kernel/Makefile > @@ -141,6 +141,8 @@ obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o > > obj-$(CONFIG_X86_INTEL_CET) += cet.o > > +obj-$(CONFIG_ARCH_HAS_PROGRAM_PROPERTIES) += elf.o Same thing here, enablement of program properties per se seems rather generic. > diff --git a/arch/x86/kernel/elf.c b/arch/x86/kernel/elf.c > new file mode 100644 > index 000000000000..2fddd0bc545b > --- /dev/null > +++ b/arch/x86/kernel/elf.c > @@ -0,0 +1,340 @@ > +/* 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->property[]. > + */ > + > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > + > +/* > + * 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 > + * }; > + * char n_name[4]; --> always 'GNU\0' > + * > + * struct { > + * struct property_x86 { > + * u32 pr_type; > + * u32 pr_datasz; > + * }; > + * u8 pr_data[pr_datasz]; > + * }[]; > + */ > + > +#define BUF_SIZE (PAGE_SIZE / 4) > + > +struct property_x86 { > + u32 pr_type; > + u32 pr_datasz; > +}; > + > +typedef bool (test_fn)(void *buf, u32 *arg); > +typedef void *(next_fn)(void *buf, u32 *arg); > + > +static inline bool test_note_type_0(void *buf, u32 *arg) > +{ > + struct elf_note *n = buf; > + > + return ((n->n_namesz == 4) && (memcmp(n + 1, "GNU", 4) == 0) && > + (n->n_type == NT_GNU_PROPERTY_TYPE_0)); > +} > + > +static inline void *next_note(void *buf, u32 *arg) > +{ > + struct elf_note *n = buf; > + u32 align = *arg; > + int size; > + > + size = round_up(sizeof(*n) + n->n_namesz, align); > + size = round_up(size + n->n_descsz, align); > + > + if (buf + size < buf) > + return NULL; > + else > + return (buf + size); > +} > + > +static inline bool test_property_x86(void *buf, u32 *arg) > +{ > + struct property_x86 *pr = buf; > + u32 max_type = *arg; > + > + if (pr->pr_type > max_type) > + *arg = pr->pr_type; > + > + return (pr->pr_type == GNU_PROPERTY_X86_FEATURE_1_AND); > +} > + > +static inline void *next_property(void *buf, u32 *arg) > +{ > + struct property_x86 *pr = buf; > + u32 max_type = *arg; > + > + if ((buf + sizeof(*pr) + pr->pr_datasz < buf) || > + (pr->pr_type > GNU_PROPERTY_X86_FEATURE_1_AND) || > + (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_fn test, next_fn next, u32 *arg, 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(p, arg)) { > + found = 1; > + break; > + } > + > + p = next(p, arg); > + } > + > + *pos = (p + item_size <= buf) ? 0 : (u32)(p - buf); > + return found; > +} > + > +/* > + * Search a NT_GNU_PROPERTY_TYPE_0 for GNU_PROPERTY_X86_FEATURE_1_AND. > + */ > +static int find_feature_x86(struct file *file, unsigned long desc_size, > + loff_t file_offset, u8 *buf, u32 *feature) > +{ > + u32 buf_pos; > + unsigned long read_size; > + unsigned long done; > + int found = 0; > + int ret = 0; > + u32 last_pr = 0; > + > + *feature = 0; > + buf_pos = 0; > + > + 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 property_x86), > + test_property_x86, next_property, > + &last_pr, &buf_pos); > + > + if ((!buf_pos) || found) > + break; > + > + file_offset += buf_pos - read_size; > + } > + > + if (found) { > + struct property_x86 *pr = > + (struct property_x86 *)(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) { > + *feature = *data; > + } else { > + file_offset += buf_pos - read_size; > + file_offset += sizeof(*pr); > + ret = kernel_read(file, feature, 4, > + &file_offset); > + } > + } > + } > + > + return ret; > +} > + > +/* > + * Search a PT_NOTE segment for the first NT_GNU_PROPERTY_TYPE_0. > + */ > +static int find_note_type_0(struct file *file, unsigned long note_size, > + loff_t file_offset, u32 align, u32 *feature) > +{ > + u8 *buf; > + u32 buf_pos; > + unsigned long read_size; > + unsigned long done; > + int found = 0; > + int ret = 0; > + > + buf = kmalloc(BUF_SIZE, GFP_KERNEL); > + if (!buf) > + return -ENOMEM; > + > + *feature = 0; > + buf_pos = 0; > + > + for (done = 0; done < note_size; done += buf_pos) { > + read_size = note_size - done; > + if (read_size > BUF_SIZE) > + read_size = BUF_SIZE; > + > + ret = kernel_read(file, buf, read_size, &file_offset); > + > + if (ret != read_size) { > + ret = (ret < 0) ? ret : -EIO; > + kfree(buf); > + return ret; > + } > + > + /* > + * item_size = sizeof(struct elf_note) + elf_note.n_namesz. > + * n_namesz is 4 for the note type we look for. > + */ > + ret = 0; > + found += scan(buf, read_size, sizeof(struct elf_note) + 4, > + test_note_type_0, next_note, > + &align, &buf_pos); > + > + file_offset += buf_pos - read_size; > + > + if (found == 1) { > + struct elf_note *n = > + (struct elf_note *)(buf + buf_pos); > + u32 start = round_up(sizeof(*n) + n->n_namesz, align); > + u32 total = round_up(start + n->n_descsz, align); > + > + ret = find_feature_x86(file, n->n_descsz, > + file_offset + start, > + buf, feature); > + file_offset += total; > + buf_pos += total; > + } else if (!buf_pos) { > + *feature = 0; > + break; > + } > + } > + > + kfree(buf); > + return ret; > +} > + > +#ifdef CONFIG_COMPAT > +static int check_notes_32(struct file *file, struct elf32_phdr *phdr, > + int phnum, u32 *feature) > +{ > + int i; > + int err = 0; > + > + for (i = 0; i < phnum; i++, phdr++) { > + if ((phdr->p_type != PT_NOTE) || (phdr->p_align != 4)) > + continue; > + > + err = find_note_type_0(file, phdr->p_filesz, phdr->p_offset, > + phdr->p_align, feature); > + if (err) > + return err; > + } > + > + return 0; > +} > +#endif > + > +#ifdef CONFIG_X86_64 > +static int check_notes_64(struct file *file, struct elf64_phdr *phdr, > + int phnum, u32 *feature) > +{ > + int i; > + int err = 0; > + > + for (i = 0; i < phnum; i++, phdr++) { > + if ((phdr->p_type != PT_NOTE) || (phdr->p_align != 8)) > + continue; > + > + err = find_note_type_0(file, phdr->p_filesz, phdr->p_offset, > + phdr->p_align, feature); > + if (err) > + return err; > + } > + > + return 0; > +} > +#endif > + > +int arch_setup_features(void *ehdr_p, void *phdr_p, > + struct file *file, bool interp) > +{ > + int err = 0; > + u32 feature = 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_notes_64(file, phdr64, ehdr64->e_phnum, > + &feature); > + 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_notes_32(file, phdr32, ehdr32->e_phnum, > + &feature); > + if (err < 0) > + goto out; > + } > +#endif > + } > + > + memset(¤t->thread.cet, 0, sizeof(struct cet_status)); > + > + if (cpu_feature_enabled(X86_FEATURE_SHSTK)) { > + if (feature & GNU_PROPERTY_X86_FEATURE_1_SHSTK) { > + err = cet_setup_shstk(); > + if (err < 0) > + goto out; > + } > + } > + > +out: > + return err; > +} There's a lot of similar code with bpf stackmap .build-id code (commit v4.17-rc1~148^2~156^2~3^2~1), it might be worthy generalising some ELF traversal routines, since there's general need of parsing ELF property segments.