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* [glibc] x32: Handle displacement overflow in PLT rewrite [BZ #31218]
@ 2024-01-06 22:26 H.J. Lu
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From: H.J. Lu @ 2024-01-06 22:26 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=0f9afc265a4a0f4ba658d7f71c9602a3fda3538e
commit 0f9afc265a4a0f4ba658d7f71c9602a3fda3538e
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Sat Jan 6 14:03:37 2024 -0800
x32: Handle displacement overflow in PLT rewrite [BZ #31218]
PLT rewrite calculated displacement with
ElfW(Addr) disp = value - branch_start - JMP32_INSN_SIZE;
On x32, displacement from 0xf7fbe060 to 0x401030 was calculated as
unsigned int disp = 0x401030 - 0xf7fbe060 - 5;
with disp == 0x8442fcb and caused displacement overflow. The PLT entry
was changed to:
0xf7fbe060 <+0>: e9 cb 2f 44 08 jmp 0x401030
0xf7fbe065 <+5>: cc int3
0xf7fbe066 <+6>: cc int3
0xf7fbe067 <+7>: cc int3
0xf7fbe068 <+8>: cc int3
0xf7fbe069 <+9>: cc int3
0xf7fbe06a <+10>: cc int3
0xf7fbe06b <+11>: cc int3
0xf7fbe06c <+12>: cc int3
0xf7fbe06d <+13>: cc int3
0xf7fbe06e <+14>: cc int3
0xf7fbe06f <+15>: cc int3
x32 has 32-bit address range, but it doesn't wrap address around at 4GB,
JMP target was changed to 0x100401030 (0xf7fbe060LL + 0x8442fcbLL + 5),
which is above 4GB.
Always use uint64_t to calculate displacement. This fixes BZ #31218.
Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
Diff:
---
sysdeps/x86_64/Makefile | 8 +++++++
sysdeps/x86_64/dl-machine.h | 5 ++--
sysdeps/x86_64/tst-plt-rewrite2.c | 46 ++++++++++++++++++++++++++++++++++++
sysdeps/x86_64/tst-plt-rewritemod2.c | 32 +++++++++++++++++++++++++
4 files changed, 89 insertions(+), 2 deletions(-)
diff --git a/sysdeps/x86_64/Makefile b/sysdeps/x86_64/Makefile
index 374bca80d0..836e03a224 100644
--- a/sysdeps/x86_64/Makefile
+++ b/sysdeps/x86_64/Makefile
@@ -186,9 +186,11 @@ endif
ifeq (yes,$(have-z-mark-plt))
tests += \
tst-plt-rewrite1 \
+ tst-plt-rewrite2 \
# tests
modules-names += \
tst-plt-rewritemod1 \
+ tst-plt-rewritemod2 \
# modules-names
tst-plt-rewrite1-no-pie = yes
@@ -200,6 +202,12 @@ $(objpfx)tst-plt-rewrite1.out: /dev/null $(objpfx)tst-plt-rewrite1
$(tst-plt-rewrite1-ENV) $(make-test-out) > $@ 2>&1; \
grep -q -E "changing 'bar' PLT entry in .*/elf/tst-plt-rewritemod1.so' to direct branch" $@; \
$(evaluate-test)
+
+tst-plt-rewrite2-no-pie = yes
+LDFLAGS-tst-plt-rewrite2 = -Wl,-z,now
+LDFLAGS-tst-plt-rewritemod2.so = -Wl,-z,now,-z,undefs
+tst-plt-rewrite2-ENV = GLIBC_TUNABLES=glibc.cpu.plt_rewrite=2
+$(objpfx)tst-plt-rewrite2: $(objpfx)tst-plt-rewritemod2.so
endif
endif # $(subdir) == elf
diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
index ca290ef082..2d2ce503a5 100644
--- a/sysdeps/x86_64/dl-machine.h
+++ b/sysdeps/x86_64/dl-machine.h
@@ -607,8 +607,9 @@ x86_64_rewrite_plt (struct link_map *map, ElfW(Addr) plt_rewrite)
/* Skip ENDBR64 if IBT isn't enabled. */
if (!ibt_enabled_p)
branch_start = ALIGN_DOWN (branch_start, pltent);
- /* Get the displacement from the branch target. */
- ElfW(Addr) disp = value - branch_start - JMP32_INSN_SIZE;
+ /* Get the displacement from the branch target. NB: We must use
+ 64-bit integer on x32 to avoid overflow. */
+ uint64_t disp = (uint64_t) value - branch_start - JMP32_INSN_SIZE;
ElfW(Addr) plt_end;
ElfW(Addr) pad;
diff --git a/sysdeps/x86_64/tst-plt-rewrite2.c b/sysdeps/x86_64/tst-plt-rewrite2.c
new file mode 100644
index 0000000000..8427df5605
--- /dev/null
+++ b/sysdeps/x86_64/tst-plt-rewrite2.c
@@ -0,0 +1,46 @@
+/* Test PLT rewrite with 32-bit displacement overflow.
+ Copyright (C) 2024 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <support/check.h>
+
+extern int (*func_p) (void);
+extern void foo (void);
+
+int
+func (void)
+{
+ return 0xbadbeef;
+}
+
+void
+bar (void)
+{
+ TEST_VERIFY (func_p == &func);
+ TEST_VERIFY (func_p () == 0xbadbeef);
+}
+
+static int
+do_test (void)
+{
+ func_p = &func;
+ foo ();
+ bar ();
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/x86_64/tst-plt-rewritemod2.c b/sysdeps/x86_64/tst-plt-rewritemod2.c
new file mode 100644
index 0000000000..4a86d736b5
--- /dev/null
+++ b/sysdeps/x86_64/tst-plt-rewritemod2.c
@@ -0,0 +1,32 @@
+/* Check PLT rewrite with 32-bit displacement overflow.
+ Copyright (C) 2024 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+/* foo calls func with indirect branch via PLT. PLT rewrite shouldn't
+ change it to direct branch if func is too far way. */
+
+#include <support/check.h>
+
+int (*func_p) (void);
+extern int func (void);
+
+void
+foo (void)
+{
+ TEST_VERIFY (func () == 0xbadbeef);
+ TEST_VERIFY (func_p () == 0xbadbeef);
+}
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