The commit https://github.com/cloudius-systems/osv/commit/f5cc12d56dd986d2c7982c5738b1f859702b07fb addressed the issue #993 to relax handling of missing symbols in relocate_pltgot() when loading ELF objects with BIND_NOW. This patch on other hand attempts to close the gap of handling missing symbols this time in relocate_rela() during loading phase of ELF objects by dynamic linker.
The solution is similar to what we do in relocate_pltgot() - let missing symbol get ignored and hope they will not be used. However in this case we cannot rely on lazy symbol resolution logic that would catch missing symbol later when used and abort. Instead we place an indicator of missing symbol (special invalid address) which would trigger page fault when symbol accessed. This indicator allows us to distinguish missing symbol used scenario from other page fault related ones. This unfortunately does not tell us which missing symbol was used. In future we could place indicator + offset where offset would point to a name of the missing symbol in some missing symbols table. Fixes #1023 Signed-off-by: Waldemar Kozaczuk <[email protected]> --- arch/x64/arch-elf.cc | 20 ++++++++++++++++---- arch/x64/arch-elf.hh | 2 ++ arch/x64/mmu.cc | 4 ++++ 3 files changed, 22 insertions(+), 4 deletions(-) diff --git a/arch/x64/arch-elf.cc b/arch/x64/arch-elf.cc index ebe40996..4c513150 100644 --- a/arch/x64/arch-elf.cc +++ b/arch/x64/arch-elf.cc @@ -70,16 +70,28 @@ bool object::arch_relocate_rela(u32 type, u32 sym, void *addr, memcpy(addr, sm.relocated_addr(), sm.size()); break; } - case R_X86_64_64: - *static_cast<void**>(addr) = symbol(sym).relocated_addr() + addend; + case R_X86_64_64: { + auto _sym = symbol(sym, true); + if (_sym.symbol) { + *static_cast<void**>(addr) = _sym.relocated_addr() + addend; + } else { + *static_cast<void**>(addr) = MISSING_SYMBOL_INDICATOR; + } break; + } case R_X86_64_RELATIVE: *static_cast<void**>(addr) = _base + addend; break; case R_X86_64_JUMP_SLOT: - case R_X86_64_GLOB_DAT: - *static_cast<void**>(addr) = symbol(sym).relocated_addr(); + case R_X86_64_GLOB_DAT: { + auto _sym = symbol(sym, true); + if (_sym.symbol) { + *static_cast<void**>(addr) = _sym.relocated_addr(); + } else { + *static_cast<void**>(addr) = MISSING_SYMBOL_INDICATOR; + } break; + } // The next 3 types are intended to relocate symbols of thread local variables // defined with __thread modifier // diff --git a/arch/x64/arch-elf.hh b/arch/x64/arch-elf.hh index 1811ceb5..b4c63967 100644 --- a/arch/x64/arch-elf.hh +++ b/arch/x64/arch-elf.hh @@ -34,6 +34,8 @@ enum { R_X86_64_IRELATIVE = 37, // word64 indirect(B + A) }; +void * const MISSING_SYMBOL_INDICATOR = (void*)0xffffeeeeddddcccc; + /* for pltgot relocation */ #define ARCH_JUMP_SLOT R_X86_64_JUMP_SLOT diff --git a/arch/x64/mmu.cc b/arch/x64/mmu.cc index 2f1ba5e2..441b6c45 100644 --- a/arch/x64/mmu.cc +++ b/arch/x64/mmu.cc @@ -6,6 +6,7 @@ */ #include "arch-cpu.hh" +#include "arch-elf.hh" #include <osv/debug.hh> #include <osv/sched.hh> #include <osv/mmu.hh> @@ -28,6 +29,9 @@ void page_fault(exception_frame *ef) if (!pc) { abort("trying to execute null pointer"); } + if (pc == MISSING_SYMBOL_INDICATOR) { + abort("trying to execute missing symbol"); + } // The following code may sleep. So let's verify the fault did not happen // when preemption was disabled, or interrupts were disabled. assert(sched::preemptable()); -- 2.20.1 -- You received this message because you are subscribed to the Google Groups "OSv Development" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/osv-dev/20190820042043.25133-1-jwkozaczuk%40gmail.com.
