diff mbox series

[v2] ld.so: Always use MAP_COPY to map the first segment [BZ #30452]

Message ID 20230622213031.746114-1-hjl.tools@gmail.com
State New
Headers show
Series [v2] ld.so: Always use MAP_COPY to map the first segment [BZ #30452] | expand

Commit Message

H.J. Lu June 22, 2023, 9:30 p.m. UTC 
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

Andreas Schwab June 29, 2023, 11:32 a.m. UTC | #1 
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.
diff mbox series

Patch

diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
index 504cfc0a41..ac10182d58 100644
--- a/elf/dl-map-segments.h
+++ b/elf/dl-map-segments.h
@@ -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;
diff --git a/sysdeps/x86_64/64/Makefile b/sysdeps/x86_64/64/Makefile
index 73fcfe0bb0..17f0081b19 100644
--- a/sysdeps/x86_64/64/Makefile
+++ b/sysdeps/x86_64/64/Makefile
@@ -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
diff --git a/sysdeps/x86_64/64/tst-map-32bit-2.c b/sysdeps/x86_64/64/tst-map-32bit-2.c
new file mode 100644
index 0000000000..34ab01c773
--- /dev/null
+++ b/sysdeps/x86_64/64/tst-map-32bit-2.c
@@ -0,0 +1 @@ 
+#include "tst-map-32bit-1a.c"
diff --git a/sysdeps/x86_64/64/tst-map-32bit-mod-2.c b/sysdeps/x86_64/64/tst-map-32bit-mod-2.c
new file mode 100644
index 0000000000..69e795c024
--- /dev/null
+++ b/sysdeps/x86_64/64/tst-map-32bit-mod-2.c
@@ -0,0 +1 @@ 
+#include "tst-map-32bit-mod.c"