[libunwind] r352016 - [libunwind] Don't abort if encoutering invalid .eh_frame_hdr

[Hans Wennborg via cfe-commits]

It seems like a good change, so merged in r353287. Please let me know
if you have any concerns.

On Tue, Jan 29, 2019 at 3:11 PM Hans Wennborg <hans at chromium.org> wrote:
>
> Should we merge this to 8.0?
>
> On Wed, Jan 23, 2019 at 10:04 PM Petr Hosek via cfe-commits
> <cfe-commits at lists.llvm.org> wrote:
> >
> > Author: phosek
> > Date: Wed Jan 23 19:04:42 2019
> > New Revision: 352016
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=352016&view=rev
> > Log:
> > [libunwind] Don't abort if encoutering invalid .eh_frame_hdr
> >
> > Recent Linux kernel release has introduced a bug as part of the ORC
> > rollout where the vDSO has a valid .eh_frame section, but it's missing
> > the .eh_frame_hdr section and GNU_EH_FRAME segment has zero size. This
> > causes libunwind to abort which breaks programs that use libunwind.
> >
> > The other unwinder implementation (libgcc, non-gnu) instead silently
> > bail out unless being compiled as debug. This change modifies libunwind
> > to use the same strategy.
> >
> > Differential Revision: https://reviews.llvm.org/D57081
> >
> > Modified:
> >     libunwind/trunk/src/AddressSpace.hpp
> >     libunwind/trunk/src/EHHeaderParser.hpp
> >
> > Modified: libunwind/trunk/src/AddressSpace.hpp
> > URL: http://llvm.org/viewvc/llvm-project/libunwind/trunk/src/AddressSpace.hpp?rev=352016&r1=352015&r2=352016&view=diff
> > ==============================================================================
> > --- libunwind/trunk/src/AddressSpace.hpp (original)
> > +++ libunwind/trunk/src/AddressSpace.hpp Wed Jan 23 19:04:42 2019
> > @@ -535,11 +535,11 @@ inline bool LocalAddressSpace::findUnwin
> >  #endif
> >              cbdata->sects->dwarf_index_section = eh_frame_hdr_start;
> >              cbdata->sects->dwarf_index_section_length = phdr->p_memsz;
> > -            EHHeaderParser<LocalAddressSpace>::decodeEHHdr(
> > +            found_hdr = EHHeaderParser<LocalAddressSpace>::decodeEHHdr(
> >                  *cbdata->addressSpace, eh_frame_hdr_start, phdr->p_memsz,
> >                  hdrInfo);
> > -            cbdata->sects->dwarf_section = hdrInfo.eh_frame_ptr;
> > -            found_hdr = true;
> > +            if (found_hdr)
> > +              cbdata->sects->dwarf_section = hdrInfo.eh_frame_ptr;
> >            }
> >          }
> >
> >
> > Modified: libunwind/trunk/src/EHHeaderParser.hpp
> > URL: http://llvm.org/viewvc/llvm-project/libunwind/trunk/src/EHHeaderParser.hpp?rev=352016&r1=352015&r2=352016&view=diff
> > ==============================================================================
> > --- libunwind/trunk/src/EHHeaderParser.hpp (original)
> > +++ libunwind/trunk/src/EHHeaderParser.hpp Wed Jan 23 19:04:42 2019
> > @@ -35,7 +35,7 @@ public:
> >      uint8_t table_enc;
> >    };
> >
> > -  static void decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
> > +  static bool decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
> >                            EHHeaderInfo &ehHdrInfo);
> >    static bool findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
> >                        uint32_t sectionLength,
> > @@ -52,12 +52,14 @@ private:
> >  };
> >
> >  template <typename A>
> > -void EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
> > +bool EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
> >                                      pint_t ehHdrEnd, EHHeaderInfo &ehHdrInfo) {
> >    pint_t p = ehHdrStart;
> >    uint8_t version = addressSpace.get8(p++);
> > -  if (version != 1)
> > -    _LIBUNWIND_ABORT("Unsupported .eh_frame_hdr version");
> > +  if (version != 1) {
> > +    _LIBUNWIND_LOG0("Unsupported .eh_frame_hdr version");
> > +    return false;
> > +  }
> >
> >    uint8_t eh_frame_ptr_enc = addressSpace.get8(p++);
> >    uint8_t fde_count_enc = addressSpace.get8(p++);
> > @@ -70,6 +72,8 @@ void EHHeaderParser<A>::decodeEHHdr(A &a
> >            ? 0
> >            : addressSpace.getEncodedP(p, ehHdrEnd, fde_count_enc, ehHdrStart);
> >    ehHdrInfo.table = p;
> > +
> > +  return true;
> >  }
> >
> >  template <typename A>
> > @@ -101,7 +105,9 @@ bool EHHeaderParser<A>::findFDE(A &addre
> >    pint_t ehHdrEnd = ehHdrStart + sectionLength;
> >
> >    EHHeaderParser<A>::EHHeaderInfo hdrInfo;
> > -  EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd, hdrInfo);
> > +  if (!EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd,
> > +                                      hdrInfo))
> > +    return false;
> >
> >    size_t tableEntrySize = getTableEntrySize(hdrInfo.table_enc);
> >    pint_t tableEntry;
> >
> >
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