[PATCH v2 02/12] ELF: Add ELF program property parsing support

From: Dave Martin
Date: Thu Oct 10 2019 - 14:45:39 EST

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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@xxxxxxx>

---

[Dropped Kees' Reviewed-by -- rework in parse_elf_property() needs
review.]

Changes since RFC v2:

* Rework parse_elf_property() for clearer tracking the current parsing
cursor in the property data.

o is now the current offset into data.

datasz is now kept updated to reflect the amount of data _remaining_
starting at offset o. This hopefully makes
"next item size > remaining data size" checks more intuitive.

The final offset is assigned back to *off on success, as before.

* Rename elf*_gnu_property_align #defines to upper case, to reflect
the fact that these are contants, not type name aliases.
---
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 c5642bc..ae345f6 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
@@ -670,6 +676,111 @@ 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(*off > datasz || *off % ELF_GNU_PROPERTY_ALIGN))
+ return -EIO;
+ o = *off;
+ datasz -= *off;
+
+ if (datasz < sizeof(*pr))
+ return -EIO;
+ pr = (const struct gnu_property *)(data + o);
+ o += sizeof(*pr);
+ datasz -= sizeof(*pr);
+
+ if (pr->pr_datasz > datasz)
+ return -EIO;
+
+ WARN_ON(o % ELF_GNU_PROPERTY_ALIGN);
+ step = round_up(pr->pr_datasz, ELF_GNU_PROPERTY_ALIGN);
+ if (step > datasz)
+ return -EIO;
+
+ /* Properties are supposed to be unique and sorted on pr_type: */
+ if (have_prev_type && pr->pr_type <= *prev_type)
+ return -EIO;
+ *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(phdr->p_type != PT_GNU_PROPERTY))
+ return -EIO;
+
+ /* 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 -EIO;
+
+ off = round_up(sizeof(note.nhdr) + NOTE_NAME_SZ,
+ ELF_GNU_PROPERTY_ALIGN);
+ if (off > n)
+ return -EIO;
+
+ if (note.nhdr.n_descsz > n - off)
+ return -EIO;
+ 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 */
@@ -677,6 +788,7 @@ 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;
@@ -724,6 +836,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
char *elf_interpreter;
loff_t pos;

+ if (elf_ppnt->p_type == PT_GNU_PROPERTY) {
+ elf_property_phdata = elf_ppnt;
+ continue;
+ }
+
if (elf_ppnt->p_type != PT_INTERP)
continue;

@@ -819,9 +936,14 @@ 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,
@@ -832,6 +954,11 @@ 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 b7f9ffa..67896e0 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 459cddc..7bdc6da 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

@@ -64,4 +69,18 @@ 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 c377314..20900f4 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 */
--
2.1.4

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