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From 718fdd87b1b98ef88e883a37d9c18867256fa5a4 Mon Sep 17 00:00:00 2001
From: Rongwei Wang <rongwei.wang@linux.alibaba.com>
Date: Fri, 10 Dec 2021 20:39:10 +0800
Subject: [PATCH] elf: Properly align PT_LOAD segments [BZ #28676]
When PT_LOAD segment alignment > the page size, allocate enough space to
ensure that the segment can be properly aligned. This change helps code
segments use huge pages become simple and available.
This fixes [BZ #28676].
Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com>
---
elf/dl-load.c | 2 ++
elf/dl-load.h | 3 ++-
elf/dl-map-segments.h | 50 +++++++++++++++++++++++++++++++++++++++----
3 files changed, 50 insertions(+), 5 deletions(-)
diff --git a/elf/dl-load.c b/elf/dl-load.c
index bf8957e73c..721593135e 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1,5 +1,6 @@
/* Map in a shared object's segments from the file.
Copyright (C) 1995-2021 Free Software Foundation, Inc.
+ Copyright The GNU Toolchain Authors.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -1150,6 +1151,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
c->dataend = ph->p_vaddr + ph->p_filesz;
c->allocend = ph->p_vaddr + ph->p_memsz;
+ c->mapalign = ph->p_align;
c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
/* Determine whether there is a gap between the last segment
diff --git a/elf/dl-load.h b/elf/dl-load.h
index e329d49a81..e6dabcb336 100644
--- a/elf/dl-load.h
+++ b/elf/dl-load.h
@@ -1,5 +1,6 @@
/* Map in a shared object's segments from the file.
Copyright (C) 1995-2021 Free Software Foundation, Inc.
+ Copyright The GNU Toolchain Authors.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -74,7 +75,7 @@ ELF_PREFERRED_ADDRESS_DATA;
Its details have been expanded out and converted. */
struct loadcmd
{
- ElfW(Addr) mapstart, mapend, dataend, allocend;
+ ElfW(Addr) mapstart, mapend, dataend, allocend, mapalign;
ElfW(Off) mapoff;
int prot; /* PROT_* bits. */
};
diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
index f9fb110ee3..70a4c40695 100644
--- a/elf/dl-map-segments.h
+++ b/elf/dl-map-segments.h
@@ -1,5 +1,6 @@
/* Map in a shared object's segments. Generic version.
Copyright (C) 1995-2021 Free Software Foundation, Inc.
+ Copyright The GNU Toolchain Authors.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -18,6 +19,50 @@
#include <dl-load.h>
+/* Map a segment and align it properly. */
+
+static __always_inline ElfW(Addr)
+_dl_map_segment (const struct loadcmd *c, ElfW(Addr) mappref,
+ const size_t maplength, int fd)
+{
+ if (__glibc_likely (c->mapalign <= GLRO(dl_pagesize)))
+ return (ElfW(Addr)) __mmap ((void *) mappref, maplength, c->prot,
+ MAP_COPY|MAP_FILE, fd, c->mapoff);
+
+ /* If the segment alignment > the page size, allocate enough space to
+ ensure that the segment can be properly aligned. */
+ ElfW(Addr) maplen = (maplength >= c->mapalign
+ ? (maplength + c->mapalign)
+ : (2 * c->mapalign));
+ ElfW(Addr) map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen,
+ PROT_NONE,
+ MAP_ANONYMOUS|MAP_PRIVATE,
+ -1, 0);
+ if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
+ return map_start;
+
+ ElfW(Addr) map_start_aligned = ALIGN_UP (map_start, c->mapalign);
+ map_start_aligned = (ElfW(Addr)) __mmap ((void *) map_start_aligned,
+ maplength, c->prot,
+ MAP_COPY|MAP_FILE|MAP_FIXED,
+ fd, c->mapoff);
+ if (__glibc_unlikely ((void *) map_start_aligned == MAP_FAILED))
+ __munmap ((void *) map_start, maplen);
+ else
+ {
+ /* Unmap the unused regions. */
+ ElfW(Addr) delta = map_start_aligned - map_start;
+ if (delta)
+ __munmap ((void *) map_start, delta);
+ ElfW(Addr) map_end = map_start_aligned + maplength;
+ delta = map_start + maplen - map_end;
+ if (delta)
+ __munmap ((void *) map_end, delta);
+ }
+
+ return map_start_aligned;
+}
+
/* This implementation assumes (as does the corresponding implementation
of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects
are always laid out with all segments contiguous (or with gaps
@@ -53,10 +98,7 @@ _dl_map_segments (struct link_map *l, int fd,
- MAP_BASE_ADDR (l));
/* Remember which part of the address space this object uses. */
- l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength,
- c->prot,
- MAP_COPY|MAP_FILE,
- fd, c->mapoff);
+ l->l_map_start = _dl_map_segment (c, mappref, maplength, fd);
if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED))
return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT;
--
2.43.0
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