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

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

[H.J. Lu]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6259ab39410cdefc80077afea48ca9cb057f6005

commit 6259ab39410cdefc80077afea48ca9cb057f6005
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Jun 22 14:30:31 2023 -0700

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

Diff:
---
 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(-)

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"