On Wed, Mar 4, 2015 at 5:53 PM, tip-bot for Denys Vlasenko <tip...@zytor.com> wrote: > Commit-ID: 76f5df43cab5e765c0bd42289103e8f625813ae1 > Gitweb: http://git.kernel.org/tip/76f5df43cab5e765c0bd42289103e8f625813ae1 > Author: Denys Vlasenko <dvlas...@redhat.com> > AuthorDate: Thu, 26 Feb 2015 14:40:27 -0800 > Committer: Ingo Molnar <mi...@kernel.org> > CommitDate: Wed, 4 Mar 2015 22:50:49 +0100 > > x86/asm/entry/64: Always allocate a complete "struct pt_regs" on the kernel > stack > > The 64-bit entry code was using six stack slots less by not > saving/restoring registers which are callee-preserved according > to the C ABI, and was not allocating space for them. > > Only when syscalls needed a complete "struct pt_regs" was > the complete area allocated and filled in. > > As an additional twist, on interrupt entry a "slightly less > truncated pt_regs" trick is used, to make nested interrupt > stacks easier to unwind. > > This proved to be a source of significant obfuscation and subtle > bugs. For example, 'stub_fork' had to pop the return address, > extend the struct, save registers, and push return address back. > Ugly. 'ia32_ptregs_common' pops return address and "returns" via > jmp insn, throwing a wrench into CPU return stack cache. > > This patch changes the code to always allocate a complete > "struct pt_regs" on the kernel stack. The saving of registers > is still done lazily. > > "Partial pt_regs" trick on interrupt stack is retained. > > Macros which manipulate "struct pt_regs" on stack are reworked: > > - ALLOC_PT_GPREGS_ON_STACK allocates the structure. > > - SAVE_C_REGS saves to it those registers which are clobbered > by C code. > > - SAVE_EXTRA_REGS saves to it all other registers. > > - Corresponding RESTORE_* and REMOVE_PT_GPREGS_FROM_STACK macros > reverse it. > > 'ia32_ptregs_common', 'stub_fork' and friends lost their ugly dance > with the return pointer. > > LOAD_ARGS32 in ia32entry.S now uses symbolic stack offsets > instead of magic numbers. > > 'error_entry' and 'save_paranoid' now use SAVE_C_REGS + > SAVE_EXTRA_REGS instead of having it open-coded yet again. > > Patch was run-tested: 64-bit executables, 32-bit executables, > strace works. > > Timing tests did not show measurable difference in 32-bit > and 64-bit syscalls. > > Signed-off-by: Denys Vlasenko <dvlas...@redhat.com> > Signed-off-by: Andy Lutomirski <l...@amacapital.net> > Cc: Alexei Starovoitov <a...@plumgrid.com> > Cc: Borislav Petkov <b...@alien8.de> > Cc: Frederic Weisbecker <fweis...@gmail.com> > Cc: H. Peter Anvin <h...@zytor.com> > Cc: Kees Cook <keesc...@chromium.org> > Cc: Linus Torvalds <torva...@linux-foundation.org> > Cc: Oleg Nesterov <o...@redhat.com> > Cc: Will Drewry <w...@chromium.org> > Link: > http://lkml.kernel.org/r/1423778052-21038-2-git-send-email-dvlas...@redhat.com > Link: > http://lkml.kernel.org/r/b89763d354aa23e670b9bdf3a40ae320320a7c2e.1424989793.git.l...@amacapital.net > Signed-off-by: Ingo Molnar <mi...@kernel.org>
> @@ -492,7 +496,6 @@ GLOBAL(stub32_clone) > > ALIGN > ia32_ptregs_common: > - popq %r11 > CFI_ENDPROC > CFI_STARTPROC32 simple > CFI_SIGNAL_FRAME > @@ -507,9 +510,9 @@ ia32_ptregs_common: > /* CFI_REL_OFFSET rflags,EFLAGS-ARGOFFSET*/ > CFI_REL_OFFSET rsp,RSP-ARGOFFSET > /* CFI_REL_OFFSET ss,SS-ARGOFFSET*/ > - SAVE_REST > + SAVE_EXTRA_REGS 8 > call *%rax > - RESTORE_REST > - jmp ia32_sysret /* misbalances the return cache */ > + RESTORE_EXTRA_REGS 8 > + ret > CFI_ENDPROC > END(ia32_ptregs_common) This change is causing Wine to fail when it's built to support both 32-bit and 64-bit code: [ 523.657406] wineserver[1605]: segfault at 453a7c90 ip 00000000453a7c90 sp 00000000b3c6ad10 error 14 in ld-2.21.so[7fad453a7000+21000] It tries to exec the 64-bit wineserver from 32-bit code and faults because %rip is truncated. This is because simply returning to the caller will exit via sysretl which doesn't change %cs to 64-bit mode. We need to set a thread flag to enter the slow path and return via iret instead. Patch coming to fix it. -- Brian Gerst -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
