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Check multiple NT_GNU_PROPERTY_TYPE_0 notes [BZ #23509]

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Linkers group input note sections with the same name into one output
note section with the same name.  One output note section is placed in
one PT_NOTE segment.  Since new linkers merge input .note.gnu.property
sections into one output .note.gnu.property section, there is only
one NT_GNU_PROPERTY_TYPE_0 note in one PT_NOTE segment with new linkers.
Since older linkers treat input .note.gnu.property section as a generic
note section and just concatenate all input .note.gnu.property sections
into one output .note.gnu.property section without merging them, we may
see multiple NT_GNU_PROPERTY_TYPE_0 notes in one PT_NOTE segment with
older linkers.

When an older linker is used to created the program on CET-enabled OS,
the linker output has a single .note.gnu.property section with multiple
NT_GNU_PROPERTY_TYPE_0 notes, some of which have IBT and SHSTK enable
bits set even if the program isn't CET enabled.  Such programs will
crash on CET-enabled machines.  This patch updates the note parser:

1. Skip note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed.
2. Check multiple NT_GNU_PROPERTY_TYPE_0 notes.

	[BZ #23509]
	* sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Skip
	note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed.
	Update the l_cet field when processing NT_GNU_PROPERTY_TYPE_0 note.
	Check multiple NT_GNU_PROPERTY_TYPE_0 notes.
	* sysdeps/x86/link_map.h (l_cet): Expand to 3 bits,  Add
	lc_unknown.
This commit is contained in:
H.J. Lu 2018-11-08 10:06:58 -08:00
parent ac8060265b
commit d524fa6c35
3 changed files with 56 additions and 14 deletions
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10
ChangeLog
View File

@ -1,3 +1,13 @@
2018-11-08 H.J. Lu <hongjiu.lu@intel.com>
[BZ #23509]
* sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Skip
note parsing if a NT_GNU_PROPERTY_TYPE_0 note has been processed.
Update the l_cet field when processing NT_GNU_PROPERTY_TYPE_0 note.
Check multiple NT_GNU_PROPERTY_TYPE_0 notes.
* sysdeps/x86/link_map.h (l_cet): Expand to 3 bits, Add
lc_unknown.
2018-11-08 Alexandra Hájková <ahajkova@redhat.com>
[BZ #17630]

51
sysdeps/x86/dl-prop.h
View File

@ -49,6 +49,10 @@ _dl_process_cet_property_note (struct link_map *l,
const ElfW(Addr) align)
{
#if CET_ENABLED
/* Skip if we have seen a NT_GNU_PROPERTY_TYPE_0 note before. */
if (l->l_cet != lc_unknown)
return;
/* The NT_GNU_PROPERTY_TYPE_0 note must be aliged to 4 bytes in
32-bit objects and to 8 bytes in 64-bit objects. Skip notes
with incorrect alignment. */
@ -57,6 +61,9 @@ _dl_process_cet_property_note (struct link_map *l,
const ElfW(Addr) start = (ElfW(Addr)) note;
unsigned int feature_1 = 0;
unsigned int last_type = 0;
while ((ElfW(Addr)) (note + 1) - start < size)
{
/* Find the NT_GNU_PROPERTY_TYPE_0 note. */
@ -64,10 +71,18 @@ _dl_process_cet_property_note (struct link_map *l,
&& note->n_type == NT_GNU_PROPERTY_TYPE_0
&& memcmp (note + 1, "GNU", 4) == 0)
{
/* Stop if we see more than one GNU property note which may
be generated by the older linker. */
if (l->l_cet != lc_unknown)
return;
/* Check CET status now. */
l->l_cet = lc_none;
/* Check for invalid property. */
if (note->n_descsz < 8
|| (note->n_descsz % sizeof (ElfW(Addr))) != 0)
break;
return;
/* Start and end of property array. */
unsigned char *ptr = (unsigned char *) (note + 1) + 4;
@ -78,9 +93,15 @@ _dl_process_cet_property_note (struct link_map *l,
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)
break;
return;
last_type = type;
if (type == GNU_PROPERTY_X86_FEATURE_1_AND)
{
@ -89,14 +110,18 @@ _dl_process_cet_property_note (struct link_map *l,
we stop the search regardless if its size is correct
or not. There is no point to continue if this note
is ill-formed. */
if (datasz == 4)
{
unsigned int feature_1 = *(unsigned int *) ptr;
if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_IBT))
l->l_cet |= lc_ibt;
if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_SHSTK))
l->l_cet |= lc_shstk;
}
if (datasz != 4)
return;
feature_1 = *(unsigned int *) ptr;
/* Keep searching for the next GNU property note
generated by the older linker. */
break;
}
else if (type > GNU_PROPERTY_X86_FEATURE_1_AND)
{
/* Stop since property type is in ascending order. */
return;
}
@ -112,6 +137,12 @@ _dl_process_cet_property_note (struct link_map *l,
+ ELF_NOTE_NEXT_OFFSET (note->n_namesz, note->n_descsz,
align));
}
/* We get here only if there is one or no GNU property note. */
if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_IBT))
l->l_cet |= lc_ibt;
if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_SHSTK))
l->l_cet |= lc_shstk;
#endif
}

9
sysdeps/x86/link_map.h
View File

@ -19,8 +19,9 @@
/* If this object is enabled with CET. */
enum
{
lc_none = 0, /* Not enabled with CET. */
lc_ibt = 1 << 0, /* Enabled with IBT. */
lc_shstk = 1 << 1, /* Enabled with STSHK. */
lc_unknown = 0, /* Unknown CET status. */
lc_none = 1 << 0, /* Not enabled with CET. */
lc_ibt = 1 << 1, /* Enabled with IBT. */
lc_shstk = 1 << 2, /* Enabled with STSHK. */
lc_ibt_and_shstk = lc_ibt | lc_shstk /* Enabled with both. */
} l_cet:2;
} l_cet:3;