Re: [PATCH v9 02/13] ELF: Add ELF program property parsing support

Kees Cook
2020-03-12T23:59:28Z

On Wed, Mar 11, 2020 at 07:25:57PM +0000, Mark Brown wrote:
> From: Dave Martin <Dave.Martin@arm.com>
>
> ELF program properties will be needed for detecting whether to
> enable optional architecture or ABI features for a new ELF process.
>
> For now, there are no generic properties that we care about, so do
> nothing unless CONFIG_ARCH_USE_GNU_PROPERTY=y.
>
> Otherwise, the presence of properties using the PT_PROGRAM_PROPERTY
> phdrs entry (if any), and notify each property to the arch code.
>
> For now, the added code is not used.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> Signed-off-by: Mark Brown <broonie@kernel.org>

I think my review got lost along the way. Please consider this:

Reviewed-by: Kees Cook <keescook@chromium.org>

Thanks!

-Kees

> ---
> fs/binfmt_elf.c | 127 +++++++++++++++++++++++++++++++++++++++
> fs/compat_binfmt_elf.c | 4 ++
> include/linux/elf.h | 19 ++++++
> include/uapi/linux/elf.h | 4 ++
> 4 files changed, 154 insertions(+)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index f4713ea76e82..1fb67e506b68 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -39,12 +39,18 @@
> #include <linux/sched/coredump.h>
> #include <linux/sched/task_stack.h>
> #include <linux/sched/cputime.h>
> +#include <linux/sizes.h>
> +#include <linux/types.h>
> #include <linux/cred.h>
> #include <linux/dax.h>
> #include <linux/uaccess.h>
> #include <asm/param.h>
> #include <asm/page.h>
>
> +#ifndef ELF_COMPAT
> +#define ELF_COMPAT 0
> +#endif
> +
> #ifndef user_long_t
> #define user_long_t long
> #endif
> @@ -681,6 +687,111 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
> * libraries. There is no binary dependent code anywhere else.
> */
>
> +static int parse_elf_property(const char *data, size_t *off, size_t datasz,
> + struct arch_elf_state *arch,
> + bool have_prev_type, u32 *prev_type)
> +{
> + size_t o, step;
> + const struct gnu_property *pr;
> + int ret;
> +
> + if (*off == datasz)
> + return -ENOENT;
> +
> + if (WARN_ON_ONCE(*off > datasz || *off % ELF_GNU_PROPERTY_ALIGN))
> + return -EIO;
> + o = *off;
> + datasz -= *off;
> +
> + if (datasz < sizeof(*pr))
> + return -ENOEXEC;
> + pr = (const struct gnu_property *)(data + o);
> + o += sizeof(*pr);
> + datasz -= sizeof(*pr);
> +
> + if (pr->pr_datasz > datasz)
> + return -ENOEXEC;
> +
> + WARN_ON_ONCE(o % ELF_GNU_PROPERTY_ALIGN);
> + step = round_up(pr->pr_datasz, ELF_GNU_PROPERTY_ALIGN);
> + if (step > datasz)
> + return -ENOEXEC;
> +
> + /* Properties are supposed to be unique and sorted on pr_type: */
> + if (have_prev_type && pr->pr_type <= *prev_type)
> + return -ENOEXEC;
> + *prev_type = pr->pr_type;
> +
> + ret = arch_parse_elf_property(pr->pr_type, data + o,
> + pr->pr_datasz, ELF_COMPAT, arch);
> + if (ret)
> + return ret;
> +
> + *off = o + step;
> + return 0;
> +}
> +
> +#define NOTE_DATA_SZ SZ_1K
> +#define GNU_PROPERTY_TYPE_0_NAME "GNU"
> +#define NOTE_NAME_SZ (sizeof(GNU_PROPERTY_TYPE_0_NAME))
> +
> +static int parse_elf_properties(struct file *f, const struct elf_phdr *phdr,
> + struct arch_elf_state *arch)
> +{
> + union {
> + struct elf_note nhdr;
> + char data[NOTE_DATA_SZ];
> + } note;
> + loff_t pos;
> + ssize_t n;
> + size_t off, datasz;
> + int ret;
> + bool have_prev_type;
> + u32 prev_type;
> +
> + if (!IS_ENABLED(CONFIG_ARCH_USE_GNU_PROPERTY) || !phdr)
> + return 0;
> +
> + /* load_elf_binary() shouldn't call us unless this is true... */
> + if (WARN_ON_ONCE(phdr->p_type != PT_GNU_PROPERTY))
> + return -ENOEXEC;
> +
> + /* If the properties are crazy large, that's too bad (for now): */
> + if (phdr->p_filesz > sizeof(note))
> + return -ENOEXEC;
> +
> + pos = phdr->p_offset;
> + n = kernel_read(f, &note, phdr->p_filesz, &pos);
> +
> + BUILD_BUG_ON(sizeof(note) < sizeof(note.nhdr) + NOTE_NAME_SZ);
> + if (n < 0 || n < sizeof(note.nhdr) + NOTE_NAME_SZ)
> + return -EIO;
> +
> + if (note.nhdr.n_type != NT_GNU_PROPERTY_TYPE_0 ||
> + note.nhdr.n_namesz != NOTE_NAME_SZ ||
> + strncmp(note.data + sizeof(note.nhdr),
> + GNU_PROPERTY_TYPE_0_NAME, n - sizeof(note.nhdr)))
> + return -ENOEXEC;
> +
> + off = round_up(sizeof(note.nhdr) + NOTE_NAME_SZ,
> + ELF_GNU_PROPERTY_ALIGN);
> + if (off > n)
> + return -ENOEXEC;
> +
> + if (note.nhdr.n_descsz > n - off)
> + return -ENOEXEC;
> + datasz = off + note.nhdr.n_descsz;
> +
> + have_prev_type = false;
> + do {
> + ret = parse_elf_property(note.data, &off, datasz, arch,
> + have_prev_type, &prev_type);
> + have_prev_type = true;
> + } while (!ret);
> +
> + return ret == -ENOENT ? 0 : ret;
> +}
> +
> static int load_elf_binary(struct linux_binprm *bprm)
> {
> struct file *interpreter = NULL; /* to shut gcc up */
> @@ -688,6 +799,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> int load_addr_set = 0;
> unsigned long error;
> struct elf_phdr *elf_ppnt, *elf_phdata, *interp_elf_phdata = NULL;
> + struct elf_phdr *elf_property_phdata = NULL;
> unsigned long elf_bss, elf_brk;
> int bss_prot = 0;
> int retval, i;
> @@ -733,6 +845,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
> for (i = 0; i < elf_ex->e_phnum; i++, elf_ppnt++) {
> char *elf_interpreter;
>
> + if (elf_ppnt->p_type == PT_GNU_PROPERTY) {
> + elf_property_phdata = elf_ppnt;
> + continue;
> + }
> +
> if (elf_ppnt->p_type != PT_INTERP)
> continue;
>
> @@ -820,9 +937,14 @@ static int load_elf_binary(struct linux_binprm *bprm)
> goto out_free_dentry;
>
> /* Pass PT_LOPROC..PT_HIPROC headers to arch code */
> + elf_property_phdata = NULL;
> elf_ppnt = interp_elf_phdata;
> for (i = 0; i < loc->interp_elf_ex.e_phnum; i++, elf_ppnt++)
> switch (elf_ppnt->p_type) {
> + case PT_GNU_PROPERTY:
> + elf_property_phdata = elf_ppnt;
> + break;
> +
> case PT_LOPROC ... PT_HIPROC:
> retval = arch_elf_pt_proc(&loc->interp_elf_ex,
> elf_ppnt, interpreter,
> @@ -833,6 +955,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
> }
> }
>
> + retval = parse_elf_properties(interpreter ?: bprm->file,
> + elf_property_phdata, &arch_state);
> + if (retval)
> + goto out_free_dentry;
> +
> /*
> * Allow arch code to reject the ELF at this point, whilst it's
> * still possible to return an error to the code that invoked
> diff --git a/fs/compat_binfmt_elf.c b/fs/compat_binfmt_elf.c
> index aaad4ca1217e..13a087bc816b 100644
> --- a/fs/compat_binfmt_elf.c
> +++ b/fs/compat_binfmt_elf.c
> @@ -17,6 +17,8 @@
> #include <linux/elfcore-compat.h>
> #include <linux/time.h>
>
> +#define ELF_COMPAT 1
> +
> /*
> * Rename the basic ELF layout types to refer to the 32-bit class of files.
> */
> @@ -28,11 +30,13 @@
> #undef elf_shdr
> #undef elf_note
> #undef elf_addr_t
> +#undef ELF_GNU_PROPERTY_ALIGN
> #define elfhdr elf32_hdr
> #define elf_phdr elf32_phdr
> #define elf_shdr elf32_shdr
> #define elf_note elf32_note
> #define elf_addr_t Elf32_Addr
> +#define ELF_GNU_PROPERTY_ALIGN ELF32_GNU_PROPERTY_ALIGN
>
> /*
> * Some data types as stored in coredump.
> diff --git a/include/linux/elf.h b/include/linux/elf.h
> index f7b24c5fcfb6..db5113479f5e 100644
> --- a/include/linux/elf.h
> +++ b/include/linux/elf.h
> @@ -22,6 +22,9 @@
> SET_PERSONALITY(ex)
> #endif
>
> +#define ELF32_GNU_PROPERTY_ALIGN 4
> +#define ELF64_GNU_PROPERTY_ALIGN 8
> +
> #if ELF_CLASS == ELFCLASS32
>
> extern Elf32_Dyn _DYNAMIC [];
> @@ -32,6 +35,7 @@ extern Elf32_Dyn _DYNAMIC [];
> #define elf_addr_t Elf32_Off
> #define Elf_Half Elf32_Half
> #define Elf_Word Elf32_Word
> +#define ELF_GNU_PROPERTY_ALIGN ELF32_GNU_PROPERTY_ALIGN
>
> #else
>
> @@ -43,6 +47,7 @@ extern Elf64_Dyn _DYNAMIC [];
> #define elf_addr_t Elf64_Off
> #define Elf_Half Elf64_Half
> #define Elf_Word Elf64_Word
> +#define ELF_GNU_PROPERTY_ALIGN ELF64_GNU_PROPERTY_ALIGN
>
> #endif
>
> @@ -68,4 +73,18 @@ struct gnu_property {
> u32 pr_datasz;
> };
>
> +struct arch_elf_state;
> +
> +#ifndef CONFIG_ARCH_USE_GNU_PROPERTY
> +static inline int arch_parse_elf_property(u32 type, const void *data,
> + size_t datasz, bool compat,
> + 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);
> +#endif
> +
> #endif /* _LINUX_ELF_H */
> diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
> index c37731407074..20900f4496b7 100644
> --- a/include/uapi/linux/elf.h
> +++ b/include/uapi/linux/elf.h
> @@ -368,6 +368,7 @@ typedef struct elf64_shdr {
> * Notes used in ET_CORE. Architectures export some of the arch register sets
> * using the corresponding note types via the PTRACE_GETREGSET and
> * PTRACE_SETREGSET requests.
> + * The note name for all these is "LINUX".
> */
> #define NT_PRSTATUS 1
> #define NT_PRFPREG 2
> @@ -430,6 +431,9 @@ typedef struct elf64_shdr {
> #define NT_MIPS_FP_MODE 0x801 /* MIPS floating-point mode */
> #define NT_MIPS_MSA 0x802 /* MIPS SIMD registers */
>
> +/* Note types with note name "GNU" */
> +#define NT_GNU_PROPERTY_TYPE_0 5
> +
> /* Note header in a PT_NOTE section */
> typedef struct elf32_note {
> Elf32_Word n_namesz; /* Name size */
> --
> 2.20.1
>

--
Kees Cook