Messages in this thread | | | Date | Fri, 20 Mar 2015 17:21:51 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH 2/5] x86: get rid of KERNEL_STACK_OFFSET |
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On Thu, Mar 19, 2015 at 06:17:46PM +0100, Denys Vlasenko wrote: > PER_CPU_VAR(kernel_stack) was set up in a way where it points > five stack slots below the top of stack. > > Presumably, it was done to avoid one "sub $5*8,%rsp" > in syscall/sysenter code paths, where iret frame needs to be > created by hand. > > Ironically, none of them benefits from this optimization, > since all of them need to allocate additional data on stack > (struct pt_regs), so they still have to perform subtraction. > > This patch eliminates KERNEL_STACK_OFFSET. > > PER_CPU_VAR(kernel_stack) now points directly to top of stack. > pt_regs allocations are adjusted to allocate iret frame as well. > Hopefully we can merge it later with 32-bit specific > PER_CPU_VAR(cpu_current_top_of_stack) variable... > > Net result in generated code is that constants in several insns > are changed. > > This change is necessary for changing struct pt_regs creation > in SYSCALL64 code path from MOV to PUSH instructions. > > Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com> > CC: Linus Torvalds <torvalds@linux-foundation.org> > CC: Steven Rostedt <rostedt@goodmis.org> > CC: Ingo Molnar <mingo@kernel.org> > CC: Borislav Petkov <bp@alien8.de> > CC: "H. Peter Anvin" <hpa@zytor.com> > CC: Andy Lutomirski <luto@amacapital.net> > CC: Oleg Nesterov <oleg@redhat.com> > CC: Frederic Weisbecker <fweisbec@gmail.com> > CC: Alexei Starovoitov <ast@plumgrid.com> > CC: Will Drewry <wad@chromium.org> > CC: Kees Cook <keescook@chromium.org> > CC: x86@kernel.org > CC: linux-kernel@vger.kernel.org
Acked-by: Borislav Petkov <bp@suse.de>
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply. --
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