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glibc/sysdeps/hppa/dl-trampoline.S
John David Anglin 1a044511a3 Fix data race in setting function descriptors during lazy binding on hppa. 
This addresses an issue that is present mainly on SMP machines running
threaded code.  In a typical indirect call or PLT import stub, the
target address is loaded first.  Then the global pointer is loaded into
the PIC register in the delay slot of a branch to the target address.
During lazy binding, the target address is a trampoline which transfers
to _dl_runtime_resolve().

_dl_runtime_resolve() uses the relocation offset stored in the global
pointer and the linkage map stored in the trampoline to find the
relocation.  Then, the function descriptor is updated.

In a multi-threaded application, it is possible for the global pointer
to be updated between the load of the target address and the global
pointer.  When this happens, the relocation offset has been replaced
by the new global pointer.  The function pointer has probably been
updated as well but there is no way to find the address of the function
descriptor and to transfer to the target.  So, _dl_runtime_resolve()
typically crashes.

HP-UX addressed this problem by adding an extra pc-relative branch to
the trampoline.  The descriptor is initially setup to point to the
branch.  The branch then transfers to the trampoline.  This allowed
the trampoline code to figure out which descriptor was being used
without any modification to user code.  I didn't use this approach
as it is more complex and changes function pointer canonicalization.

The order of loading the target address and global pointer in
indirect calls was not consistent with the order used in import stubs.
In particular, $$dyncall and some inline versions of it loaded the
global pointer first.  This was inconsistent with the global pointer
being updated first in dl-machine.h.  Assuming the accesses are
ordered, we want elf_machine_fixup_plt() to store the global pointer
first and calls to load it last.  Then, the global pointer will be
correct when the target function is entered.

However, just to make things more fun, HP added support for
out-of-order execution of accesses in PA 2.0.  The accesses used by
calls are weakly ordered. So, it's possibly under some circumstances
that a function might be entered with the wrong global pointer.
However, HP uses weakly ordered accesses in 64-bit HP-UX, so I assume
that loading the global pointer in the delay slot of the branch must
work consistently.

The basic fix for the race is a combination of modifying user code to
preserve the address of the function descriptor in register %r22 and
setting the least-significant bit in the relocation offset.  The
latter was suggested by Carlos as a way to distinguish relocation
offsets from global pointer values.  Conventionally, %r22 is used
as the address of the function descriptor in calls to $$dyncall.
So, it wasn't hard to preserve the address in %r22.

I have updated gcc trunk and gcc-9 branch to not clobber %r22 in
$$dyncall and inline indirect calls.  I have also modified the import
stubs in binutils trunk and the 2.33 branch to preserve %r22.  This
required making the stubs one instruction longer but we save one
relocation.  I also modified binutils to align the .plt section on
a 8-byte boundary.  This allows descriptors to be updated atomically
with a floting-point store.

With these changes, _dl_runtime_resolve() can fallback to an alternate
mechanism to find the relocation offset when it has been clobbered.
There's just one additional instruction in the fast path. I tested
the fallback function, _dl_fix_reloc_arg(), by changing the branch to
always use the fallback.  Old code still runs as it did before.

Fixes bug 23296.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
2020-03-30 20:36:49 +00:00

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/* PLT trampolines. hppa version.
Copyright (C) 2005-2020 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 <sysdep.h>
/* This code gets called via the .plt stub, and is used in
dl-runtime.c to call the `_dl_fixup' function and then redirect
to the address it returns. `_dl_fixup' takes two arguments, however
`_dl_profile_fixup' takes a number of parameters for use with
library auditing (LA).
WARNING: This template is also used by gcc's __cffc, and expects
that the "bl" for _dl_runtime_resolve exist at a particular offset.
Do not change this template without changing gcc, while the prefix
"bl" should fix everything so gcc finds the right spot, it will
slow down __cffc when it attempts to call fixup to resolve function
descriptor references. Please refer to gcc/gcc/config/pa/fptr.c
Enter with r19 = reloc offset, r20 = got-8, r21 = fixup ltp, r22 = fp. */
/* RELOCATION MARKER: bl to provide gcc's __cffc with fixup loc. */
.text
/* THIS CODE DOES NOT EXECUTE */
bl _dl_fixup, %r2
.text
.global _dl_runtime_resolve
.type _dl_runtime_resolve,@function
cfi_startproc
.align 4
_dl_runtime_resolve:
.PROC
.CALLINFO FRAME=128,CALLS,SAVE_RP,ENTRY_GR=3
.ENTRY
/* SAVE_RP says we do */
stw %rp, -20(%sp)
/* Save static link register */
stw %r29,-16(%sp)
/* Save argument registers */
stw %r26,-36(%sp)
stw %r25,-40(%sp)
stw %r24,-44(%sp)
stw %r23,-48(%sp)
/* Build a call frame, and save structure pointer. */
copy %sp, %r1 /* Copy previous sp */
/* Save function result address (on entry) */
stwm %r28,128(%sp)
/* Fill in some frame info to follow ABI */
stw %r1,-4(%sp) /* Previous sp */
stw %r21,-32(%sp) /* PIC register value */
/* Save input floating point registers. This must be done
in the new frame since the previous frame doesn't have
enough space */
ldo -64(%sp),%r1
fstd,ma %fr4,-8(%r1)
fstd,ma %fr5,-8(%r1)
fstd,ma %fr6,-8(%r1)
/* Test PA_GP_RELOC bit. */
bb,>= %r19,31,2f /* branch if not reloc offset */
fstd,ma %fr7,-8(%r1)
/* Set up args to fixup func, needs only two arguments */
ldw 8+4(%r20),%r26 /* (1) got[1] == struct link_map */
copy %r19,%r25 /* (2) reloc offset */
/* Call the real address resolver. */
3: bl _dl_fixup,%rp
copy %r21,%r19 /* set fixup func ltp */
/* While the linker will set a function pointer to NULL when it
encounters an undefined weak function, we need to dynamically
detect removed weak functions. The issue arises because a weak
__gmon_start__ function was added to shared executables to work
around issues in _init that are now resolved. The presence of
__gmon_start__ in every shared library breaks the linker
`--as-needed' option. This __gmon_start__ function does nothing
but removal is tricky. Depending on the binding, removal can
cause an application using it to fault. The call to _dl_fixup
returns NULL when a function isn't resolved. In order to help
with __gmon_start__ removal, we return directly to the caller
when _dl_fixup returns NULL. This check could be removed when
BZ 19170 is fixed. */
comib,= 0,%r28,1f
/* Load up the returned func descriptor */
copy %r28, %r22
copy %r29, %r19
/* Reload arguments fp args */
ldo -64(%sp),%r1
fldd,ma -8(%r1),%fr4
fldd,ma -8(%r1),%fr5
fldd,ma -8(%r1),%fr6
fldd,ma -8(%r1),%fr7
/* Adjust sp, and restore function result address*/
ldwm -128(%sp),%r28
/* Reload static link register */
ldw -16(%sp),%r29
/* Reload general args */
ldw -36(%sp),%r26
ldw -40(%sp),%r25
ldw -44(%sp),%r24
ldw -48(%sp),%r23
/* Jump to new function, but return to previous function */
bv %r0(%r22)
ldw -20(%sp),%rp
1:
/* Return to previous function */
ldw -148(%sp),%rp
bv %r0(%rp)
ldo -128(%sp),%sp
2:
/* Set up args for _dl_fix_reloc_arg. */
copy %r22,%r26 /* (1) function pointer */
depi 0,31,2,%r26 /* clear least significant bits */
ldw 8+4(%r20),%r25 /* (2) got[1] == struct link_map */
/* Save ltp and link map arg for _dl_fixup. */
stw %r21,-56(%sp) /* ltp */
stw %r25,-60(%sp) /* struct link map */
/* Find reloc offset. */
bl _dl_fix_reloc_arg,%rp
copy %r21,%r19 /* set func ltp */
/* Set up args for _dl_fixup. */
ldw -56(%sp),%r21 /* ltp */
ldw -60(%sp),%r26 /* (1) struct link map */
b 3b
copy %ret0,%r25 /* (2) reloc offset */
.EXIT
.PROCEND
cfi_endproc
.size _dl_runtime_resolve, . - _dl_runtime_resolve
.text
.global _dl_runtime_profile
.type _dl_runtime_profile,@function
cfi_startproc
.align 4
_dl_runtime_profile:
.PROC
.CALLINFO FRAME=192,CALLS,SAVE_RP,ENTRY_GR=3
.ENTRY
/* SAVE_RP says we do */
stw %rp, -20(%sp)
/* Save static link register */
stw %r29,-16(%sp)
/* Build a call frame, and save structure pointer. */
copy %sp, %r1 /* Copy previous sp */
/* Save function result address (on entry) */
stwm %r28,192(%sp)
/* Fill in some frame info to follow ABI */
stw %r1,-4(%sp) /* Previous sp */
stw %r21,-32(%sp) /* PIC register value */
/* Create La_hppa_retval */
/* -140, lrv_r28
-136, lrv_r29
-132, 4 byte pad
-128, lr_fr4 (8 bytes) */
/* Create save space for _dl_profile_fixup arguments
-120, Saved reloc offset
-116, Saved struct link_map
-112, *framesizep */
/* Create La_hppa_regs */
/* 32-bit registers */
stw %r26,-108(%sp)
stw %r25,-104(%sp)
stw %r24,-100(%sp)
stw %r23,-96(%sp)
/* -92, 4 byte pad */
/* 64-bit floating point registers */
ldo -88(%sp),%r1
fstd,ma %fr4,8(%r1)
fstd,ma %fr5,8(%r1)
fstd,ma %fr6,8(%r1)
fstd,ma %fr7,8(%r1)
/* Test PA_GP_RELOC bit. */
bb,>= %r19,31,2f /* branch if not reloc offset */
/* 32-bit stack pointer */
stw %sp,-56(%sp)
/* Set up args to fixup func, needs five arguments */
ldw 8+4(%r20),%r26 /* (1) got[1] == struct link_map */
stw %r26,-116(%sp) /* Save struct link_map */
copy %r19,%r25 /* (2) reloc offset */
stw %r25,-120(%sp) /* Save reloc offset */
copy %rp,%r24 /* (3) profile_fixup needs rp */
ldo -56(%sp),%r23 /* (4) La_hppa_regs */
ldo -112(%sp), %r1
stw %r1, -52(%sp) /* (5) long int *framesizep */
/* Call the real address resolver. */
3: bl _dl_profile_fixup,%rp
copy %r21,%r19 /* set fixup func ltp */
/* Load up the returned function descriptor */
copy %r28, %r22
copy %r29, %r19
/* Restore gr/fr/sp/rp */
ldw -108(%sp),%r26
ldw -104(%sp),%r25
ldw -100(%sp),%r24
ldw -96(%sp),%r23
/* -92, 4 byte pad, skip */
ldo -88(%sp),%r1
fldd,ma 8(%r1),%fr4
fldd,ma 8(%r1),%fr5
fldd,ma 8(%r1),%fr6
fldd,ma 8(%r1),%fr7
/* Reload rp register -(192+20) without adjusting stack */
ldw -212(%sp),%rp
/* Reload static link register -(192+16) without adjusting stack */
ldw -208(%sp),%r29
/* *framesizep is >= 0 if we have to run pltexit */
ldw -112(%sp),%r28
cmpb,>>=,N %r0,%r28,L(cpe)
/* Adjust sp, and restore function result address*/
ldwm -192(%sp),%r28
/* Jump to new function, but return to previous function */
bv %r0(%r22)
ldw -20(%sp),%rp
/* NO RETURN */
L(nf):
/* Call the returned function descriptor */
bv %r0(%r22)
nop
b,n L(cont)
L(cpe):
/* We are going to call the resolved function, but we have a
stack frame in the middle. We use the value of framesize to
guess how much extra frame we need, and how much frame to
copy forward. */
/* Round to nearest multiple of 64 */
addi 63, %r28, %r28
depi 0, 27, 6, %r28
/* Calcualte start of stack copy */
ldo -192(%sp),%r2
/* Increate the stack by *framesizep */
copy %sp, %r1
add %sp, %r28, %sp
/* Save stack pointer */
stw %r1, -4(%sp)
/* Single byte copy of prevous stack onto newly allocated stack */
1: ldb %r28(%r2), %r1
add %r28, %sp, %r26
stb %r1, 0(%r26)
addi,< -1,%r28,%r28
b,n 1b
/* Retore r28 and r27 and r2 already points at -192(%sp) */
ldw 0(%r2),%r28
ldw 84(%r2),%r26
/* Calculate address of L(cont) */
b,l L(nf),%r2
depwi 0,31,2,%r2
L(cont):
/* Undo fake stack */
ldw -4(%sp),%r1
copy %r1, %sp
/* Arguments to _dl_call_pltexit */
ldw -116(%sp), %r26 /* (1) got[1] == struct link_map */
ldw -120(%sp), %r25 /* (2) reloc offsets */
ldo -56(%sp), %r24 /* (3) *La_hppa_regs */
ldo -124(%sp), %r23 /* (4) *La_hppa_retval */
/* Fill *La_hppa_retval */
stw %r28,-140(%sp)
stw %r29,-136(%sp)
ldo -128(%sp), %r1
fstd %fr4,0(%r1)
/* Call _dl_call_pltexit */
bl _dl_call_pltexit,%rp
nop
/* Restore *La_hppa_retval */
ldw -140(%sp), %r28
ldw -136(%sp), %r29
ldo -128(%sp), %r1
fldd 0(%r1), %fr4
/* Unwind the stack */
ldo 192(%sp),%sp
/* Retore callers rp */
ldw -20(%sp),%rp
/* Return */
bv,n 0(%r2)
2:
/* Set up args for _dl_fix_reloc_arg. */
copy %r22,%r26 /* (1) function pointer */
depi 0,31,2,%r26 /* clear least significant bits */
ldw 8+4(%r20),%r25 /* (2) got[1] == struct link_map */
/* Save ltp and link map arg for _dl_fixup. */
stw %r21,-92(%sp) /* ltp */
stw %r25,-116(%sp) /* struct link map */
/* Find reloc offset. */
bl _dl_fix_reloc_arg,%rp
copy %r21,%r19 /* set func ltp */
/* Restore fixup ltp. */
ldw -92(%sp),%r21 /* ltp */
/* Set up args to fixup func, needs five arguments */
ldw -116(%sp),%r26 /* (1) struct link map */
copy %ret0,%r25 /* (2) reloc offset */
stw %r25,-120(%sp) /* Save reloc offset */
ldw -212(%sp),%r24 /* (3) profile_fixup needs rp */
ldo -56(%sp),%r23 /* (4) La_hppa_regs */
ldo -112(%sp), %r1
b 3b
stw %r1, -52(%sp) /* (5) long int *framesizep */
.EXIT
.PROCEND
cfi_endproc
.size _dl_runtime_profile, . - _dl_runtime_profile
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