<[email protected]>,Chris Metcalf <[email protected]>,"Paul E . McKenney" <[email protected]>,Andrew Morton <[email protected]>,Christopher Li <[email protected]>,Dou Liyang <[email protected]>,Masahiro Yamada <[email protected]>,Daniel Borkmann <[email protected]>,Markus Trippelsdorf <[email protected]>,Peter Foley <[email protected]>,Steven Rostedt <[email protected]>,Tim Chen <[email protected]>,Catalin Marinas <[email protected]>,Matthew Wilcox <[email protected]>,Michal Hocko <[email protected]>,Rob Landley <[email protected]>,Jiri Kosina <[email protected]>,"H . J . Lu" <[email protected]>,Paul Bolle <[email protected]>,Baoquan He <[email protected]>,Daniel Micay <[email protected]>,the arch/x86 maintainers <[email protected]>,"[email protected]" <[email protected]>,Linux Kernel Mailing List <[email protected]>,[email protected],kvm list <[email protected]>,linux-pm <[email protected]>,linux-arch <[email protected]>,Linux-Sparse <[email protected]>,Kernel Hardening <[email protected]> From: [email protected] Message-ID: <[email protected]>
On July 19, 2017 3:58:07 PM PDT, Ard Biesheuvel <[email protected]> wrote: >On 19 July 2017 at 23:27, H. Peter Anvin <[email protected]> wrote: >> On 07/19/17 08:40, Thomas Garnier wrote: >>>> >>>> This doesn't look right. It's accessing a per-cpu variable. The >>>> per-cpu section is an absolute, zero-based section and not subject >to >>>> relocation. >>> >>> PIE does not respect the zero-based section, it tries to have >>> everything relative. Patch 16/22 also adapt per-cpu to work with PIE >>> (while keeping the zero absolute design by default). >>> >> >> This is silly. The right thing is for PIE is to be explicitly >absolute, >> without (%rip). The use of (%rip) memory references for percpu is >just >> an optimization. >> > >Sadly, there is an issue in binutils that may prevent us from doing >this as cleanly as we would want. > >For historical reasons, bfd.ld emits special symbols like >__GLOBAL_OFFSET_TABLE__ as absolute symbols with a section index of >SHN_ABS, even though it is quite obvious that they are relative like >any other symbol that points into the image. Unfortunately, this means >that binutils needs to emit R_X86_64_RELATIVE relocations even for >SHN_ABS symbols, which means we lose the ability to use both absolute >and relocatable symbols in the same PIE image (unless the reloc tool >can filter them out) > >More info here: >https://sourceware.org/bugzilla/show_bug.cgi?id=19818 The reloc tool already has the ability to filter symbols. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
