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ld.so: Always use MAP_COPY to map the first segment [BZ #30452]

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The first segment in a shared library may be read-only, not executable.
To support LD_PREFER_MAP_32BIT_EXEC on such shared libraries, we also
check MAP_DENYWRITE to decide if MAP_32BIT should be passed to mmap.
Normally the first segment is mapped with MAP_COPY, which is defined
as (MAP_PRIVATE | MAP_DENYWRITE).  But if the segment alignment is
greater than the page size, MAP_COPY isn't used to allocate enough
space to ensure that the segment can be properly aligned.  Map the
first segment with MAP_COPY in this case to fix BZ #30452.
This commit is contained in:
H.J. Lu 2023-06-22 14:30:31 -07:00
parent 9401024e5e
commit 6259ab3941
4 changed files with 10 additions and 1 deletions
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2
elf/dl-map-segments.h
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@ -36,7 +36,7 @@ _dl_map_segment (const struct loadcmd *c, ElfW(Addr) mappref,
: (2 * c->mapalign));
ElfW(Addr) map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen,
PROT_NONE,
MAP_ANONYMOUS|MAP_PRIVATE,
MAP_ANONYMOUS|MAP_COPY,
-1, 0);
if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
return map_start;

7
sysdeps/x86_64/64/Makefile
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@ -3,13 +3,16 @@ ifeq ($(subdir),elf)
tests-map-32bit = \
tst-map-32bit-1a \
tst-map-32bit-1b \
tst-map-32bit-2 \
# tests-map-32bit
tst-map-32bit-1a-no-pie = yes
tst-map-32bit-1b-no-pie = yes
tst-map-32bit-2-no-pie = yes
tests += $(tests-map-32bit)
modules-map-32bit = \
tst-map-32bit-mod \
tst-map-32bit-mod-2 \
# modules-map-32bit
modules-names += $(modules-map-32bit)
@ -18,5 +21,9 @@ tst-map-32bit-1a-ENV = LD_PREFER_MAP_32BIT_EXEC=1
$(objpfx)tst-map-32bit-1a: $(objpfx)tst-map-32bit-mod.so
tst-map-32bit-1b-ENV = GLIBC_TUNABLES=glibc.cpu.prefer_map_32bit_exec=1
$(objpfx)tst-map-32bit-1b: $(objpfx)tst-map-32bit-mod.so
LDFLAGS-tst-map-32bit-mod-2.so += -Wl,-z,max-page-size=0x200000
$(objpfx)tst-map-32bit-mod-2.so: $(libsupport)
tst-map-32bit-2-ENV = LD_PREFER_MAP_32BIT_EXEC=1
$(objpfx)tst-map-32bit-2: $(objpfx)tst-map-32bit-mod-2.so
endif

1
sysdeps/x86_64/64/tst-map-32bit-2.c Normal file
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@ -0,0 +1 @@
#include "tst-map-32bit-1a.c"

1
sysdeps/x86_64/64/tst-map-32bit-mod-2.c Normal file
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@ -0,0 +1 @@
#include "tst-map-32bit-mod.c"