[v2] ld.so: Always use MAP_COPY to map the first segment [BZ #30452]
Checks
Context |
Check |
Description |
redhat-pt-bot/TryBot-apply_patch |
success
|
Patch applied to master at the time it was sent
|
linaro-tcwg-bot/tcwg_glibc_build--master-aarch64 |
success
|
Testing passed
|
linaro-tcwg-bot/tcwg_glibc_build--master-arm |
success
|
Testing passed
|
linaro-tcwg-bot/tcwg_glibc_check--master-aarch64 |
success
|
Testing passed
|
linaro-tcwg-bot/tcwg_glibc_check--master-arm |
success
|
Testing passed
|
Commit Message
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.
---
elf/dl-map-segments.h | 2 +-
sysdeps/x86_64/64/Makefile | 7 +++++++
sysdeps/x86_64/64/tst-map-32bit-2.c | 1 +
sysdeps/x86_64/64/tst-map-32bit-mod-2.c | 1 +
4 files changed, 10 insertions(+), 1 deletion(-)
create mode 100644 sysdeps/x86_64/64/tst-map-32bit-2.c
create mode 100644 sysdeps/x86_64/64/tst-map-32bit-mod-2.c
Comments
On Jun 22 2023, H.J. Lu via Libc-alpha wrote:
> 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.
Ok.
@@ -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;
@@ -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
new file mode 100644
@@ -0,0 +1 @@
+#include "tst-map-32bit-1a.c"
new file mode 100644
@@ -0,0 +1 @@
+#include "tst-map-32bit-mod.c"