From: Kees Cook <keescook@chromium.org> To: Yu-cheng Yu <yu-cheng.yu@intel.com>, Andy Lutomirski <luto@amacapital.net> Cc: X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, LKML <linux-kernel@vger.kernel.org>, "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>, linux-arch <linux-arch@vger.kernel.org>, Linux API <linux-api@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>, Balbir Singh <bsingharora@gmail.com>, Cyrill Gorcunov <gorcunov@gmail.com>, Dave Hansen <dave.hansen@linux.intel.com>, Florian Weimer <fweimer@redhat.com>, "H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>, Mike Kravetz <mike.kravetz@oracle.com>, Nadav Amit <nadav.amit@gmail.com>, Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz> Subject: Re: [RFC PATCH v4 21/27] x86/cet/shstk: ELF header parsing of Shadow Stack Date: Mon, 15 Oct 2018 16:40:52 -0700 [thread overview] Message-ID: <CAGXu5jKO5Ot5VAJBMHudgx40g4N2tqhLKHeCdS7rkFj1bPaHig@mail.gmail.com> (raw) In-Reply-To: <20180921150351.20898-22-yu-cheng.yu@intel.com> On Fri, Sep 21, 2018 at 8:03 AM, Yu-cheng Yu <yu-cheng.yu@intel.com> wrote: > Look in .note.gnu.property of an ELF file and check if Shadow Stack needs > to be enabled for the task. Ah, I've been wanting this for other things too (see below). > > 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 | 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) > + > +#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-$(CONFIG_ARCH_HAS_PROGRAM_PROPERTIES) += elf.o > + > ### > # 64 bit specific files > ifeq ($(CONFIG_X86_64),y) > diff --git a/arch/x86/kernel/elf.c b/arch/x86/kernel/elf.c > new file mode 100644 > index 000000000000..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 <asm/cet.h> > +#include <asm/elf_property.h> > +#include <asm/prctl.h> > +#include <asm/processor.h> > +#include <uapi/linux/elf-em.h> > +#include <uapi/linux/prctl.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 > + * }; > + * char n_name[4]; --> always 'GNU\0' > + * > + * struct { > + * struct property_x86 { > + * u32 pr_type; > + * u32 pr_datasz; > + * }; > + * u8 pr_data[pr_datasz]; > + * }[]; > + */ Does NT_GNU_PROPERTY_TYPE_0 only ever contain property_x86 bytes? (I assume not, since there is a pr_type?) > + > +#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)); Cheaper to test n_type first... > +} > + > +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); I think this could overflow: n_namesz can be u64 for elf64_note. > + size = round_up(size + n->n_descsz, align); Same here. You may want to use check_add_overflow(), etc, an u64 types. > + > + if (buf + size < buf) > + return NULL; I don't understand this. You want to check size not exceeding the allocation, which isn't passed into this function. Checking for a full unsigned address wrap around is not sufficient to detect overflow. > + 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; Why is *arg being updated? I don't see last_pr used outside of here -- are properties required to be pr_type-ordered? > + > + 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) || Again, this "< buf" test doesn't look at all correct to me. > + (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) I'm not a fan of the short "scan", "test" and "next" names, and I really don't like an arg named "arg". Something slightly more descriptive for all of these would be nice, please. > +{ > + 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)) { These comparisons are safe due to the BUF_SIZE limit of buf_size and the only used size of item_size, but if this becomes more generic, it should be more defensive on the size calculations (e.g. make sure than "item_size < max" and then here "p < max - item_size", etc). I'd kind of rather this code walked the base type and check each for the matching feature. What is the general specification for what NT_GNU_PROPERTY_TYPE_0 contains? > + 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; Why kmalloc over stack variable? (Or, does BUF_SIZE here really need to be 1024?) > + > + *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); Same overflow notes from earlier... > + > + 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; Instead of a separate parser here, wouldn't it be a bit nicer to attach this to the existing binfmt_elf program header parsing loop: elf_ppnt = elf_phdata; for (i = 0; i < loc->elf_ex.e_phnum; i++, elf_ppnt++) switch (elf_ppnt->p_type) { case PT_GNU_STACK: ... case PT_LOPROC ... PT_HIPROC: ... > + > + 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 Should there be an #else error here? > + } > + > + memset(¤t->thread.cet, 0, sizeof(struct cet_status)); > + > + if (cpu_feature_enabled(X86_FEATURE_SHSTK)) { The CPU feature was already tested at arch_setup_features() entry. > + if (feature & GNU_PROPERTY_X86_FEATURE_1_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 efae2fb0930a..b891aa292b46 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -1081,6 +1081,21 @@ 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 c5358e0ae7c5..5ef25a565e88 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 > -- > 2.17.1 > I'd like to be using this code for a few other cases too (not just x86-specific). For example, for marking KASan binaries as needing a "legacy" memory layouts[1]. Others might be setting things like no_new_privs at exec time, etc. -Kees [1] https://lkml.kernel.org/r/CAGXu5jL1HRG7Dn9vraw8Hu7LF+69k3EDpztt1Ju7ijEzmvRdhA@mail.gmail.com -- Kees Cook Pixel Security
WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org> To: Yu-cheng Yu <yu-cheng.yu@intel.com>, Andy Lutomirski <luto@amacapital.net> Cc: X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, LKML <linux-kernel@vger.kernel.org>, "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>, linux-arch <linux-arch@vger.kernel.org>, Linux API <linux-api@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>, Balbir Singh <bsingharora@gmail.com>, Cyrill Gorcunov <gorcunov@gmail.com>, Dave Hansen <dave.hansen@linux.intel.com>, Florian Weimer <fweimer@redhat.com>, "H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>, Mike Kravetz <mike.kravetz@oracle.com>, Nadav Amit <nadav.amit@gmail.com>, Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>, Peter Zijlstra <peterz@infradead.org>, Randy Dunlap <rdunlap@infradead.org>, "Ravi V. Shankar" <ravi.v.shankar@intel.com>, Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com> Subject: Re: [RFC PATCH v4 21/27] x86/cet/shstk: ELF header parsing of Shadow Stack Date: Mon, 15 Oct 2018 16:40:52 -0700 [thread overview] Message-ID: <CAGXu5jKO5Ot5VAJBMHudgx40g4N2tqhLKHeCdS7rkFj1bPaHig@mail.gmail.com> (raw) Message-ID: <20181015234052.6KBHv-g1Vo8jNZnrzAbjBUFsdxiLsG1lEVrCpVZKSJ0@z> (raw) In-Reply-To: <20180921150351.20898-22-yu-cheng.yu@intel.com> On Fri, Sep 21, 2018 at 8:03 AM, Yu-cheng Yu <yu-cheng.yu@intel.com> wrote: > Look in .note.gnu.property of an ELF file and check if Shadow Stack needs > to be enabled for the task. Ah, I've been wanting this for other things too (see below). > > 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 | 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) > + > +#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-$(CONFIG_ARCH_HAS_PROGRAM_PROPERTIES) += elf.o > + > ### > # 64 bit specific files > ifeq ($(CONFIG_X86_64),y) > diff --git a/arch/x86/kernel/elf.c b/arch/x86/kernel/elf.c > new file mode 100644 > index 000000000000..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 <asm/cet.h> > +#include <asm/elf_property.h> > +#include <asm/prctl.h> > +#include <asm/processor.h> > +#include <uapi/linux/elf-em.h> > +#include <uapi/linux/prctl.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 > + * }; > + * char n_name[4]; --> always 'GNU\0' > + * > + * struct { > + * struct property_x86 { > + * u32 pr_type; > + * u32 pr_datasz; > + * }; > + * u8 pr_data[pr_datasz]; > + * }[]; > + */ Does NT_GNU_PROPERTY_TYPE_0 only ever contain property_x86 bytes? (I assume not, since there is a pr_type?) > + > +#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)); Cheaper to test n_type first... > +} > + > +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); I think this could overflow: n_namesz can be u64 for elf64_note. > + size = round_up(size + n->n_descsz, align); Same here. You may want to use check_add_overflow(), etc, an u64 types. > + > + if (buf + size < buf) > + return NULL; I don't understand this. You want to check size not exceeding the allocation, which isn't passed into this function. Checking for a full unsigned address wrap around is not sufficient to detect overflow. > + 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; Why is *arg being updated? I don't see last_pr used outside of here -- are properties required to be pr_type-ordered? > + > + 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) || Again, this "< buf" test doesn't look at all correct to me. > + (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) I'm not a fan of the short "scan", "test" and "next" names, and I really don't like an arg named "arg". Something slightly more descriptive for all of these would be nice, please. > +{ > + 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)) { These comparisons are safe due to the BUF_SIZE limit of buf_size and the only used size of item_size, but if this becomes more generic, it should be more defensive on the size calculations (e.g. make sure than "item_size < max" and then here "p < max - item_size", etc). I'd kind of rather this code walked the base type and check each for the matching feature. What is the general specification for what NT_GNU_PROPERTY_TYPE_0 contains? > + 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; Why kmalloc over stack variable? (Or, does BUF_SIZE here really need to be 1024?) > + > + *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); Same overflow notes from earlier... > + > + 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; Instead of a separate parser here, wouldn't it be a bit nicer to attach this to the existing binfmt_elf program header parsing loop: elf_ppnt = elf_phdata; for (i = 0; i < loc->elf_ex.e_phnum; i++, elf_ppnt++) switch (elf_ppnt->p_type) { case PT_GNU_STACK: ... case PT_LOPROC ... PT_HIPROC: ... > + > + 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 Should there be an #else error here? > + } > + > + memset(¤t->thread.cet, 0, sizeof(struct cet_status)); > + > + if (cpu_feature_enabled(X86_FEATURE_SHSTK)) { The CPU feature was already tested at arch_setup_features() entry. > + if (feature & GNU_PROPERTY_X86_FEATURE_1_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 efae2fb0930a..b891aa292b46 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -1081,6 +1081,21 @@ 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 c5358e0ae7c5..5ef25a565e88 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 > -- > 2.17.1 > I'd like to be using this code for a few other cases too (not just x86-specific). For example, for marking KASan binaries as needing a "legacy" memory layouts[1]. Others might be setting things like no_new_privs at exec time, etc. -Kees [1] https://lkml.kernel.org/r/CAGXu5jL1HRG7Dn9vraw8Hu7LF+69k3EDpztt1Ju7ijEzmvRdhA@mail.gmail.com -- Kees Cook Pixel Security
next prev parent reply other threads:[~2018-10-15 23:40 UTC|newest] Thread overview: 142+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-09-21 15:03 [RFC PATCH v4 00/27] Control Flow Enforcement: Shadow Stack Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 01/27] x86/cpufeatures: Add CPUIDs for Control-flow Enforcement Technology (CET) Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-25 16:27 ` Peter Zijlstra 2018-09-25 16:27 ` Peter Zijlstra 2018-09-25 16:29 ` Yu-cheng Yu 2018-09-25 16:29 ` Yu-cheng Yu 2018-09-28 16:51 ` Borislav Petkov 2018-09-28 16:51 ` Borislav Petkov 2018-09-28 16:56 ` Yu-cheng Yu 2018-09-28 16:56 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 02/27] x86/fpu/xstate: Change some names to separate XSAVES system and user states Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-25 16:37 ` Peter Zijlstra 2018-09-25 16:37 ` Peter Zijlstra 2018-10-02 15:29 ` Borislav Petkov 2018-10-02 15:29 ` Borislav Petkov 2018-10-02 16:21 ` Yu-cheng Yu 2018-10-02 16:21 ` Yu-cheng Yu 2018-10-02 16:30 ` Dave Hansen 2018-10-02 16:30 ` Dave Hansen 2018-10-02 16:37 ` Borislav Petkov 2018-10-02 16:37 ` Borislav Petkov 2018-10-02 16:39 ` Dave Hansen 2018-10-02 16:39 ` Dave Hansen 2018-10-02 16:43 ` Yu-cheng Yu 2018-10-02 16:43 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 03/27] x86/fpu/xstate: Enable XSAVES system states Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-25 17:03 ` Peter Zijlstra 2018-09-25 17:03 ` Peter Zijlstra 2018-09-25 17:23 ` Yu-cheng Yu 2018-09-25 17:23 ` Yu-cheng Yu 2018-10-02 17:15 ` Borislav Petkov 2018-10-02 17:15 ` Borislav Petkov 2018-10-04 15:47 ` Yu-cheng Yu 2018-10-04 15:47 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 04/27] x86/fpu/xstate: Add XSAVES system states for shadow stack Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 05/27] Documentation/x86: Add CET description Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 06/27] x86/cet: Control protection exception handler Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-10-03 10:39 ` Eugene Syromiatnikov 2018-10-03 10:39 ` Eugene Syromiatnikov 2018-10-03 16:11 ` Yu-cheng Yu 2018-10-03 16:11 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 07/27] x86/cet/shstk: Add Kconfig option for user-mode shadow stack Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 08/27] mm: Introduce VM_SHSTK for shadow stack memory Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 09/27] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-10-03 13:38 ` Matthew Wilcox 2018-10-03 13:38 ` Matthew Wilcox 2018-10-03 14:05 ` Dave Hansen 2018-10-03 14:05 ` Dave Hansen 2018-10-03 16:07 ` Yu-cheng Yu 2018-10-03 16:07 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 10/27] drm/i915/gvt: Update _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-10-03 13:19 ` Eugene Syromiatnikov 2018-10-03 13:19 ` Eugene Syromiatnikov 2018-09-21 15:03 ` [RFC PATCH v4 11/27] x86/mm: Introduce _PAGE_DIRTY_SW Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 12/27] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 13/27] x86/mm: Shadow stack page fault error checking Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 14/27] mm: Handle shadow stack page fault Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 15/27] mm: Handle THP/HugeTLB " Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 16/27] mm: Update can_follow_write_pte/pmd for shadow stack Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 17/27] mm: Introduce do_mmap_locked() Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 18/27] x86/cet/shstk: User-mode shadow stack support Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-10-03 15:08 ` Eugene Syromiatnikov 2018-10-03 15:08 ` Eugene Syromiatnikov 2018-10-03 15:12 ` Yu-cheng Yu 2018-10-03 15:12 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 19/27] x86/cet/shstk: Introduce WRUSS instruction Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-10-03 4:15 ` Eugene Syromiatnikov 2018-10-03 4:15 ` Eugene Syromiatnikov 2018-09-21 15:03 ` [RFC PATCH v4 20/27] x86/cet/shstk: Signal handling for shadow stack Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-10-03 14:36 ` Eugene Syromiatnikov 2018-10-03 14:36 ` Eugene Syromiatnikov 2018-10-03 16:46 ` Jann Horn 2018-10-03 16:46 ` Jann Horn 2018-09-21 15:03 ` [RFC PATCH v4 21/27] x86/cet/shstk: ELF header parsing of Shadow Stack Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-10-03 23:27 ` Eugene Syromiatnikov 2018-10-03 23:27 ` Eugene Syromiatnikov 2018-10-09 21:15 ` Yu-cheng Yu 2018-10-09 21:15 ` Yu-cheng Yu 2018-10-15 23:40 ` Kees Cook [this message] 2018-10-15 23:40 ` Kees Cook 2018-10-16 17:23 ` Yu-cheng Yu 2018-10-16 17:23 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 22/27] x86/cet/shstk: Handle thread shadow stack Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 23/27] mm/map: Add Shadow stack pages to memory accounting Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 16:55 ` Randy Dunlap 2018-09-21 16:55 ` Randy Dunlap 2018-09-21 17:21 ` Yu-cheng Yu 2018-09-21 17:21 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 24/27] mm/mmap: Create a guard area between VMAs Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-10-03 4:56 ` Eugene Syromiatnikov 2018-10-03 4:56 ` Eugene Syromiatnikov 2018-10-03 5:36 ` Andy Lutomirski 2018-10-03 5:36 ` Andy Lutomirski 2018-10-03 16:00 ` Yu-cheng Yu 2018-10-03 16:00 ` Yu-cheng Yu 2018-10-03 16:18 ` Andy Lutomirski 2018-10-03 16:18 ` Andy Lutomirski 2018-10-03 16:32 ` Eugene Syromiatnikov 2018-10-03 16:32 ` Eugene Syromiatnikov 2018-10-03 16:40 ` Yu-cheng Yu 2018-10-03 16:40 ` Yu-cheng Yu 2018-10-03 16:52 ` Jann Horn 2018-10-03 16:52 ` Jann Horn 2018-10-03 21:21 ` Eugene Syromiatnikov 2018-10-03 21:21 ` Eugene Syromiatnikov 2018-09-21 15:03 ` [RFC PATCH v4 25/27] mm/mmap: Prevent Shadow Stack VMA merges Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 15:03 ` [RFC PATCH v4 26/27] x86/cet/shstk: Add arch_prctl functions for Shadow Stack Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-10-03 17:57 ` Eugene Syromiatnikov 2018-10-03 17:57 ` Eugene Syromiatnikov 2018-09-21 15:03 ` [RFC PATCH v4 27/27] x86/cet/shstk: Add Shadow Stack instructions to opcode map Yu-cheng Yu 2018-09-21 15:03 ` Yu-cheng Yu 2018-09-21 22:53 ` [RFC PATCH v4 00/27] Control Flow Enforcement: Shadow Stack Dave Hansen 2018-09-21 22:53 ` Dave Hansen 2018-09-24 15:25 ` Yu-cheng Yu 2018-09-24 15:25 ` Yu-cheng Yu
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