* [musl] [PATCH] before __dls2b, call mprotect with __syscall [not found] <20220330021148.520601-1-alex_y_xu.ref@yahoo.ca> @ 2022-03-30 2:11 ` Alex Xu (Hello71) 2022-07-02 20:16 ` Rich Felker 0 siblings, 1 reply; 2+ messages in thread From: Alex Xu (Hello71) @ 2022-03-30 2:11 UTC (permalink / raw) To: musl; +Cc: Alex Xu (Hello71) if LTO is enabled, gcc hoists the call to ___errno_location outside the loop even though the access to errno is gated behind head != &ldso because ___errno_location is marked __attribute__((const)). this causes the program to crash because TLS is not yet initialized when called from __dls2. this is also possible if LTO is not enabled; even though gcc 11 doesn't do it, it is still wrong to use errno here. since the start and end are already aligned, we can simply call __syscall instead of using global errno. Fixes: e13a2b8953ef ("implement PT_GNU_RELRO support") --- I think this doesn't necessarily need to go in the next release, just sending it out for review. ldso/dynlink.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/ldso/dynlink.c b/ldso/dynlink.c index 5b9c8be4..b5a8f1f2 100644 --- a/ldso/dynlink.c +++ b/ldso/dynlink.c @@ -1356,12 +1356,14 @@ static void reloc_all(struct dso *p) do_relocs(p, laddr(p, dyn[DT_REL]), dyn[DT_RELSZ], 2); do_relocs(p, laddr(p, dyn[DT_RELA]), dyn[DT_RELASZ], 3); - if (head != &ldso && p->relro_start != p->relro_end && - mprotect(laddr(p, p->relro_start), p->relro_end-p->relro_start, PROT_READ) - && errno != ENOSYS) { - error("Error relocating %s: RELRO protection failed: %m", - p->name); - if (runtime) longjmp(*rtld_fail, 1); + if (head != &ldso && p->relro_start != p->relro_end) { + long ret = __syscall(SYS_mprotect, laddr(p, p->relro_start), + p->relro_end-p->relro_start, PROT_READ); + if (ret != 0 && ret != -ENOSYS) { + error("Error relocating %s: RELRO protection failed: %m", + p->name); + if (runtime) longjmp(*rtld_fail, 1); + } } p->relocated = 1; -- 2.35.1 ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [musl] [PATCH] before __dls2b, call mprotect with __syscall 2022-03-30 2:11 ` [musl] [PATCH] before __dls2b, call mprotect with __syscall Alex Xu (Hello71) @ 2022-07-02 20:16 ` Rich Felker 0 siblings, 0 replies; 2+ messages in thread From: Rich Felker @ 2022-07-02 20:16 UTC (permalink / raw) To: Alex Xu (Hello71); +Cc: musl On Thu, Jun 30, 2022 at 01:52:43PM -0400, Alex Xu (Hello71) wrote: > if LTO is enabled, gcc hoists the call to ___errno_location outside the > loop even though the access to errno is gated behind head != &ldso > because ___errno_location is marked __attribute__((const)). this causes > the program to crash because TLS is not yet initialized when called from > __dls2. this is also possible if LTO is not enabled; even though gcc 11 > doesn't do it, it is still wrong to use errno here. > > since the start and end are already aligned, we can simply call > __syscall instead of using global errno. > > Fixes: e13a2b8953ef ("implement PT_GNU_RELRO support") > --- > > ldso/dynlink.c | 14 ++++++++------ > 1 file changed, 8 insertions(+), 6 deletions(-) > > diff --git a/ldso/dynlink.c b/ldso/dynlink.c > index 5b9c8be4..b5a8f1f2 100644 > --- a/ldso/dynlink.c > +++ b/ldso/dynlink.c > @@ -1356,12 +1356,14 @@ static void reloc_all(struct dso *p) > do_relocs(p, laddr(p, dyn[DT_REL]), dyn[DT_RELSZ], 2); > do_relocs(p, laddr(p, dyn[DT_RELA]), dyn[DT_RELASZ], 3); > > - if (head != &ldso && p->relro_start != p->relro_end && > - mprotect(laddr(p, p->relro_start), p->relro_end-p->relro_start, PROT_READ) > - && errno != ENOSYS) { > - error("Error relocating %s: RELRO protection failed: %m", > - p->name); > - if (runtime) longjmp(*rtld_fail, 1); > + if (head != &ldso && p->relro_start != p->relro_end) { > + long ret = __syscall(SYS_mprotect, laddr(p, p->relro_start), > + p->relro_end-p->relro_start, PROT_READ); > + if (ret != 0 && ret != -ENOSYS) { > + error("Error relocating %s: RELRO protection failed: %m", > + p->name); > + if (runtime) longjmp(*rtld_fail, 1); > + } > } > > p->relocated = 1; > -- > 2.35.1 I think it's ok to go ahead and make this change since it's an improvement, but it looks like it's not actually a complete fix, because the call to error() is still there, which *itself* has a path to evaluation of errno via printf. A complete fix probably needs to make reloc_all take a function pointer to the error function as an argument, with __dls2 passing in a dummy function that just crashes. Rich ^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2022-07-02 20:16 UTC | newest] Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <20220330021148.520601-1-alex_y_xu.ref@yahoo.ca> 2022-03-30 2:11 ` [musl] [PATCH] before __dls2b, call mprotect with __syscall Alex Xu (Hello71) 2022-07-02 20:16 ` Rich Felker
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