[PATCH v5 07/14] rtld: Handle PT_GNU_PROPERTY
Szabolcs Nagy
szabolcs.nagy@arm.com
Mon Jun 22 14:00:20 GMT 2020
Add generic code to handle PT_GNU_PROPERTY notes. Unlike
_dl_process_pt_note, _dl_process_pt_gnu_property is generic,
has no failure mode (invalid content is ignored) and always
called after PT_LOAD segments are mapped. Currently only one
NT_GNU_PROPERTY_TYPE_0 note is handled, which contains target
specific properties: the _dl_process_gnu_property target hook
is called for each property.
Otherwise it follows the existing x86 note processing logic.
---
elf/dl-load.c | 81 ++++++++++++++++++++++++++++++++++++++
elf/rtld.c | 4 ++
sysdeps/generic/dl-prop.h | 19 ++++++---
sysdeps/generic/ldsodefs.h | 4 ++
sysdeps/x86/dl-prop.h | 7 ++++
5 files changed, 110 insertions(+), 5 deletions(-)
diff --git a/elf/dl-load.c b/elf/dl-load.c
index 06f2ba7264..66bd0ca0a3 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -853,6 +853,77 @@ lose (int code, int fd, const char *name, char *realname, struct link_map *l,
}
+/* Process PT_GNU_PROPERTY program header PH in module L after
+ PT_LOAD segments are mapped. Only one NT_GNU_PROPERTY_TYPE_0
+ note is handled which contains processor specific properties. */
+
+void
+_dl_process_pt_gnu_property (struct link_map *l, const ElfW(Phdr) *ph)
+{
+ const ElfW(Nhdr) *note = (const void *) (ph->p_vaddr + l->l_addr);
+ const ElfW(Addr) size = ph->p_memsz;
+ const ElfW(Addr) align = ph->p_align;
+
+ /* The NT_GNU_PROPERTY_TYPE_0 note must be aligned to 4 bytes in
+ 32-bit objects and to 8 bytes in 64-bit objects. Skip notes
+ with incorrect alignment. */
+ if (align != (__ELF_NATIVE_CLASS / 8))
+ return;
+
+ const ElfW(Addr) start = (ElfW(Addr)) note;
+ unsigned int last_type = 0;
+
+ while ((ElfW(Addr)) (note + 1) - start < size)
+ {
+ /* Find the NT_GNU_PROPERTY_TYPE_0 note. */
+ if (note->n_namesz == 4
+ && note->n_type == NT_GNU_PROPERTY_TYPE_0
+ && memcmp (note + 1, "GNU", 4) == 0)
+ {
+ /* Check for invalid property. */
+ if (note->n_descsz < 8
+ || (note->n_descsz % sizeof (ElfW(Addr))) != 0)
+ return;
+
+ /* Start and end of property array. */
+ unsigned char *ptr = (unsigned char *) (note + 1) + 4;
+ unsigned char *ptr_end = ptr + note->n_descsz;
+
+ do
+ {
+ unsigned int type = *(unsigned int *) ptr;
+ unsigned int datasz = *(unsigned int *) (ptr + 4);
+
+ /* Property type must be in ascending order. */
+ if (type < last_type)
+ return;
+
+ ptr += 8;
+ if ((ptr + datasz) > ptr_end)
+ return;
+
+ last_type = type;
+
+ /* Target specific property processing. */
+ if (_dl_process_gnu_property(l, type, datasz, ptr) == 0)
+ return;
+
+ /* Check the next property item. */
+ ptr += ALIGN_UP (datasz, sizeof (ElfW(Addr)));
+ }
+ while ((ptr_end - ptr) >= 8);
+
+ /* Only handle one NT_GNU_PROPERTY_TYPE_0. */
+ return;
+ }
+
+ note = ((const void *) note
+ + ELF_NOTE_NEXT_OFFSET (note->n_namesz, note->n_descsz,
+ align));
+ }
+}
+
+
/* Map in the shared object NAME, actually located in REALNAME, and already
opened on FD. */
@@ -1188,6 +1259,16 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
maplength, has_holes, loader);
if (__glibc_unlikely (errstring != NULL))
goto call_lose;
+
+ /* Process program headers again after load segments are mapped in
+ case processing requires accessing those segments. */
+ for (ph = phdr; ph < &phdr[l->l_phnum]; ++ph)
+ switch (ph->p_type)
+ {
+ case PT_GNU_PROPERTY:
+ _dl_process_pt_gnu_property (l, ph);
+ break;
+ }
}
if (l->l_ld == 0)
diff --git a/elf/rtld.c b/elf/rtld.c
index 882b070cc0..3ad2bf5079 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -1508,6 +1508,10 @@ of this helper program; chances are you did not intend to run this program.\n\
main_map->l_relro_size = ph->p_memsz;
break;
+ case PT_GNU_PROPERTY:
+ _dl_process_pt_gnu_property (main_map, ph);
+ break;
+
case PT_NOTE:
if (_rtld_process_pt_note (main_map, ph))
_dl_error_printf ("\
diff --git a/sysdeps/generic/dl-prop.h b/sysdeps/generic/dl-prop.h
index 6b0f2aa95a..ceb6f623ee 100644
--- a/sysdeps/generic/dl-prop.h
+++ b/sysdeps/generic/dl-prop.h
@@ -20,11 +20,11 @@
#define _DL_PROP_H
/* The following functions are used by the dynamic loader and the
- dlopen machinery to process PT_NOTE entries in the binary or
- shared object. The notes can be used to change the behaviour of
- the loader, and as such offer a flexible mechanism for hooking in
- various checks related to ABI tags or implementing "flag day" ABI
- transitions. */
+ dlopen machinery to process PT_NOTE and PT_GNU_PROPERTY entries in
+ the binary or shared object. The notes can be used to change the
+ behaviour of the loader, and as such offer a flexible mechanism
+ for hooking in various checks related to ABI tags or implementing
+ "flag day" ABI transitions. */
static inline void __attribute__ ((always_inline))
_rtld_main_check (struct link_map *m, const char *program)
@@ -51,4 +51,13 @@ _rtld_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph)
return 0;
}
+/* Called for each property in the NT_GNU_PROPERTY_TYPE_0 note of L,
+ processing of the properties continues until this returns 0. */
+static inline int __attribute__ ((always_inline))
+_dl_process_gnu_property (struct link_map *l, uint32_t type, uint32_t datasz,
+ void *data)
+{
+ return 0;
+}
+
#endif /* _DL_PROP_H */
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index d08b97a5ef..c525ffa12c 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -910,6 +910,10 @@ extern void _dl_setup_hash (struct link_map *map) attribute_hidden;
extern void _dl_rtld_di_serinfo (struct link_map *loader,
Dl_serinfo *si, bool counting);
+/* Process PT_GNU_PROPERTY program header PH in module L after
+ PT_LOAD segments are mapped. */
+void _dl_process_pt_gnu_property (struct link_map *l, const ElfW(Phdr) *ph);
+
/* Search loaded objects' symbol tables for a definition of the symbol
referred to by UNDEF. *SYM is the symbol table entry containing the
diff --git a/sysdeps/x86/dl-prop.h b/sysdeps/x86/dl-prop.h
index 516f88ea80..4a8ebc573e 100644
--- a/sysdeps/x86/dl-prop.h
+++ b/sysdeps/x86/dl-prop.h
@@ -191,4 +191,11 @@ _rtld_process_pt_note (struct link_map *l, const ElfW(Phdr) *ph)
return 0;
}
+static inline int __attribute__ ((always_inline))
+_dl_process_gnu_property (struct link_map *l, uint32_t type, uint32_t datasz,
+ void *data)
+{
+ return 0;
+}
+
#endif /* _DL_PROP_H */
--
2.17.1
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