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author | John David Anglin <danglin@gcc.gnu.org> | 2020-03-30 20:36:49 +0000 |
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committer | John David Anglin <danglin@gcc.gnu.org> | 2020-03-30 20:36:49 +0000 |
commit | 1a044511a3f9020c3f430164e0a6a77426fecd7e (patch) | |
tree | 61ff063e6fc9e522db9789e9bbeec401bca63394 /sysdeps | |
parent | ec07242c45ef8b24836c2089b0466b48f8ba2d1c (diff) | |
download | glibc-1a044511a3f9020c3f430164e0a6a77426fecd7e.tar.gz glibc-1a044511a3f9020c3f430164e0a6a77426fecd7e.tar.xz glibc-1a044511a3f9020c3f430164e0a6a77426fecd7e.zip |
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 When this happens, the relocation offset has been replaced by the new global pointer.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>
Diffstat (limited to 'sysdeps')
-rw-r--r-- | sysdeps/hppa/dl-fptr.c | 26 | ||||
-rw-r--r-- | sysdeps/hppa/dl-machine.h | 36 | ||||
-rw-r--r-- | sysdeps/hppa/dl-trampoline.S | 74 | ||||
-rw-r--r-- | sysdeps/unix/sysv/linux/hppa/atomic-machine.h | 28 |
4 files changed, 142 insertions, 22 deletions
diff --git a/sysdeps/hppa/dl-fptr.c b/sysdeps/hppa/dl-fptr.c index 0a37397284..25ca8f8463 100644 --- a/sysdeps/hppa/dl-fptr.c +++ b/sysdeps/hppa/dl-fptr.c @@ -172,8 +172,8 @@ make_fdesc (ElfW(Addr) ip, ElfW(Addr) gp) } install: - fdesc->ip = ip; fdesc->gp = gp; + fdesc->ip = ip; return (ElfW(Addr)) fdesc; } @@ -350,7 +350,9 @@ ElfW(Addr) _dl_lookup_address (const void *address) { ElfW(Addr) addr = (ElfW(Addr)) address; - unsigned int *desc, *gptr; + ElfW(Word) reloc_arg; + volatile unsigned int *desc; + unsigned int *gptr; /* Return ADDR if the least-significant two bits of ADDR are not consistent with ADDR being a linker defined function pointer. The normal value for @@ -367,7 +369,11 @@ _dl_lookup_address (const void *address) if (!_dl_read_access_allowed (desc)) return addr; - /* Load first word of candidate descriptor. It should be a pointer + /* First load the relocation offset. */ + reloc_arg = (ElfW(Word)) desc[1]; + atomic_full_barrier(); + + /* Then load first word of candidate descriptor. It should be a pointer with word alignment and point to memory that can be read. */ gptr = (unsigned int *) desc[0]; if (((unsigned int) gptr & 3) != 0 @@ -377,8 +383,8 @@ _dl_lookup_address (const void *address) /* See if descriptor requires resolution. The following trampoline is used in each global offset table for function resolution: - ldw 0(r20),r22 - bv r0(r22) + ldw 0(r20),r21 + bv r0(r21) ldw 4(r20),r21 tramp: b,l .-12,r20 depwi 0,31,2,r20 @@ -389,7 +395,15 @@ _dl_lookup_address (const void *address) if (gptr[0] == 0xea9f1fdd /* b,l .-12,r20 */ && gptr[1] == 0xd6801c1e /* depwi 0,31,2,r20 */ && (ElfW(Addr)) gptr[2] == elf_machine_resolve ()) - _dl_fixup ((struct link_map *) gptr[5], (ElfW(Word)) desc[1]); + { + struct link_map *l = (struct link_map *) gptr[5]; + + /* If gp has been resolved, we need to hunt for relocation offset. */ + if (!(reloc_arg & PA_GP_RELOC)) + reloc_arg = _dl_fix_reloc_arg (addr, l); + + _dl_fixup (l, reloc_arg); + } return (ElfW(Addr)) desc[0]; } diff --git a/sysdeps/hppa/dl-machine.h b/sysdeps/hppa/dl-machine.h index 9e98366ea3..8ecff97706 100644 --- a/sysdeps/hppa/dl-machine.h +++ b/sysdeps/hppa/dl-machine.h @@ -48,6 +48,14 @@ #define GOT_FROM_PLT_STUB (4*4) #define PLT_ENTRY_SIZE (2*4) +/* The gp slot in the function descriptor contains the relocation offset + before resolution. To distinguish between a resolved gp value and an + unresolved relocation offset we set an unused bit in the relocation + offset. This would allow us to do a synchronzied two word update + using this bit (interlocked update), but instead of waiting for the + update we simply recompute the gp value given that we know the ip. */ +#define PA_GP_RELOC 1 + /* Initialize the function descriptor table before relocations */ static inline void __hppa_init_bootstrap_fdesc_table (struct link_map *map) @@ -117,10 +125,28 @@ elf_machine_fixup_plt (struct link_map *map, lookup_t t, volatile Elf32_Addr *rfdesc = reloc_addr; /* map is the link_map for the caller, t is the link_map for the object being called */ - rfdesc[1] = value.gp; - /* Need to ensure that the gp is visible before the code - entry point is updated */ - rfdesc[0] = value.ip; + + /* We would like the function descriptor to be double word aligned. This + helps performance (ip and gp then reside on the same cache line) and + we can update the pair atomically with a single store. The linker + now ensures this alignment but we still have to handle old code. */ + if ((unsigned int)reloc_addr & 7) + { + /* Need to ensure that the gp is visible before the code + entry point is updated */ + rfdesc[1] = value.gp; + atomic_full_barrier(); + rfdesc[0] = value.ip; + } + else + { + /* Update pair atomically with floating point store. */ + union { ElfW(Word) v[2]; double d; } u; + + u.v[0] = value.ip; + u.v[1] = value.gp; + *(volatile double *)rfdesc = u.d; + } return value; } @@ -265,7 +291,7 @@ elf_machine_runtime_setup (struct link_map *l, int lazy, int profile) here. The trampoline code will load the proper LTP and pass the reloc offset to the fixup function. */ - fptr->gp = iplt - jmprel; + fptr->gp = (iplt - jmprel) | PA_GP_RELOC; } /* r_sym != 0 */ else { diff --git a/sysdeps/hppa/dl-trampoline.S b/sysdeps/hppa/dl-trampoline.S index 0114ca8b19..d0804b30c0 100644 --- a/sysdeps/hppa/dl-trampoline.S +++ b/sysdeps/hppa/dl-trampoline.S @@ -31,7 +31,7 @@ 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. */ + 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 @@ -61,17 +61,20 @@ _dl_runtime_resolve: copy %sp, %r1 /* Copy previous sp */ /* Save function result address (on entry) */ stwm %r28,128(%sp) - /* Fillin some frame info to follow ABI */ + /* 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 -56(%sp),%r1 + 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 */ @@ -79,7 +82,7 @@ _dl_runtime_resolve: copy %r19,%r25 /* (2) reloc offset */ /* Call the real address resolver. */ - bl _dl_fixup,%rp +3: bl _dl_fixup,%rp copy %r21,%r19 /* set fixup func ltp */ /* While the linker will set a function pointer to NULL when it @@ -102,7 +105,7 @@ _dl_runtime_resolve: copy %r29, %r19 /* Reload arguments fp args */ - ldo -56(%sp),%r1 + ldo -64(%sp),%r1 fldd,ma -8(%r1),%fr4 fldd,ma -8(%r1),%fr5 fldd,ma -8(%r1),%fr6 @@ -129,6 +132,25 @@ _dl_runtime_resolve: 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 @@ -153,7 +175,7 @@ _dl_runtime_profile: copy %sp, %r1 /* Copy previous sp */ /* Save function result address (on entry) */ stwm %r28,192(%sp) - /* Fillin some frame info to follow ABI */ + /* Fill in some frame info to follow ABI */ stw %r1,-4(%sp) /* Previous sp */ stw %r21,-32(%sp) /* PIC register value */ @@ -181,10 +203,11 @@ _dl_runtime_profile: fstd,ma %fr5,8(%r1) fstd,ma %fr6,8(%r1) fstd,ma %fr7,8(%r1) - /* 32-bit stack pointer and return register */ - stw %sp,-56(%sp) - stw %r2,-52(%sp) + /* 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 */ @@ -197,7 +220,7 @@ _dl_runtime_profile: stw %r1, -52(%sp) /* (5) long int *framesizep */ /* Call the real address resolver. */ - bl _dl_profile_fixup,%rp +3: bl _dl_profile_fixup,%rp copy %r21,%r19 /* set fixup func ltp */ /* Load up the returned function descriptor */ @@ -215,7 +238,9 @@ _dl_runtime_profile: fldd,ma 8(%r1),%fr5 fldd,ma 8(%r1),%fr6 fldd,ma 8(%r1),%fr7 - ldw -52(%sp),%rp + + /* 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 @@ -303,6 +328,33 @@ L(cont): 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 diff --git a/sysdeps/unix/sysv/linux/hppa/atomic-machine.h b/sysdeps/unix/sysv/linux/hppa/atomic-machine.h index 9d8ffbe860..bf61b66b70 100644 --- a/sysdeps/unix/sysv/linux/hppa/atomic-machine.h +++ b/sysdeps/unix/sysv/linux/hppa/atomic-machine.h @@ -36,9 +36,37 @@ typedef uintptr_t uatomicptr_t; typedef intmax_t atomic_max_t; typedef uintmax_t uatomic_max_t; +#define atomic_full_barrier() __sync_synchronize () + #define __HAVE_64B_ATOMICS 0 #define USE_ATOMIC_COMPILER_BUILTINS 0 +/* We use the compiler atomic load and store builtins as the generic + defines are not atomic. In particular, we need to use compare and + exchange for stores as the implementation is synthesized. */ +void __atomic_link_error (void); +#define __atomic_check_size_ls(mem) \ + if ((sizeof (*mem) != 1) && (sizeof (*mem) != 2) && sizeof (*mem) != 4) \ + __atomic_link_error (); + +#define atomic_load_relaxed(mem) \ + ({ __atomic_check_size_ls((mem)); \ + __atomic_load_n ((mem), __ATOMIC_RELAXED); }) +#define atomic_load_acquire(mem) \ + ({ __atomic_check_size_ls((mem)); \ + __atomic_load_n ((mem), __ATOMIC_ACQUIRE); }) + +#define atomic_store_relaxed(mem, val) \ + do { \ + __atomic_check_size_ls((mem)); \ + __atomic_store_n ((mem), (val), __ATOMIC_RELAXED); \ + } while (0) +#define atomic_store_release(mem, val) \ + do { \ + __atomic_check_size_ls((mem)); \ + __atomic_store_n ((mem), (val), __ATOMIC_RELEASE); \ + } while (0) + /* XXX Is this actually correct? */ #define ATOMIC_EXCHANGE_USES_CAS 1 |