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Message-Id: <1424822419-10267-6-git-send-email-dvlasenk@redhat.com> Date: Wed, 25 Feb 2015 01:00:18 +0100 From: Denys Vlasenko <dvlasenk@...hat.com> To: Andy Lutomirski <luto@...capital.net> Cc: Denys Vlasenko <dvlasenk@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>, Frederic Weisbecker <fweisbec@...il.com>, Alexei Starovoitov <ast@...mgrid.com>, Will Drewry <wad@...omium.org>, Kees Cook <keescook@...omium.org>, x86@...nel.org, linux-kernel@...r.kernel.org Subject: [PATCH 6/7 v2] x86: save r11 into pt_regs->eflags on SYSCALL64 fastpath Before this patch, r11 was saved in pt_regs->r11. Which looks natural, but requires messy shuffling to/from iret frame whenever ptrace or e.g. iopl wants to modify flags- because that's how this register are used by SYSCALL/SYSRET. This patch saves r11 in pt_regs->flags, and uses that value for SYSRET64 insn. Shuffling is eliminated. stub_iopl is no longer needed: pt_regs->flags needs no fixing up. Testing shows that syscall fast path is ~54.3 ns before and after the patch (on 2.7 GHz Sandy Bridge CPU). Changes since v1: better comments and commit message Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com> CC: Linus Torvalds <torvalds@...ux-foundation.org> CC: Steven Rostedt <rostedt@...dmis.org> CC: Ingo Molnar <mingo@...nel.org> CC: Borislav Petkov <bp@...en8.de> CC: "H. Peter Anvin" <hpa@...or.com> CC: Andy Lutomirski <luto@...capital.net> CC: Oleg Nesterov <oleg@...hat.com> CC: Frederic Weisbecker <fweisbec@...il.com> CC: Alexei Starovoitov <ast@...mgrid.com> CC: Will Drewry <wad@...omium.org> CC: Kees Cook <keescook@...omium.org> CC: x86@...nel.org CC: linux-kernel@...r.kernel.org --- arch/x86/include/asm/calling.h | 20 ++++++++++++++------ arch/x86/kernel/entry_64.S | 37 +++++++++++-------------------------- arch/x86/syscalls/syscall_64.tbl | 2 +- arch/x86/um/sys_call_table_64.c | 2 +- 4 files changed, 27 insertions(+), 34 deletions(-) diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h index f1a962f..4b5f7bf 100644 --- a/arch/x86/include/asm/calling.h +++ b/arch/x86/include/asm/calling.h @@ -95,9 +95,11 @@ For 32-bit we have the following conventions - kernel is built with CFI_ADJUST_CFA_OFFSET 15*8+\addskip .endm - .macro SAVE_C_REGS_HELPER offset=0 rax=1 rcx=1 r8plus=1 - .if \r8plus + .macro SAVE_C_REGS_HELPER offset=0 rax=1 rcx=1 r8910=1 r11=1 + .if \r11 movq_cfi r11, 6*8+\offset + .endif + .if \r8910 movq_cfi r10, 7*8+\offset movq_cfi r9, 8*8+\offset movq_cfi r8, 9*8+\offset @@ -113,16 +115,19 @@ For 32-bit we have the following conventions - kernel is built with movq_cfi rdi, 14*8+\offset .endm .macro SAVE_C_REGS offset=0 - SAVE_C_REGS_HELPER \offset, 1, 1, 1 + SAVE_C_REGS_HELPER \offset, 1, 1, 1, 1 .endm .macro SAVE_C_REGS_EXCEPT_RAX_RCX offset=0 - SAVE_C_REGS_HELPER \offset, 0, 0, 1 + SAVE_C_REGS_HELPER \offset, 0, 0, 1, 1 .endm .macro SAVE_C_REGS_EXCEPT_R891011 - SAVE_C_REGS_HELPER 0, 1, 1, 0 + SAVE_C_REGS_HELPER 0, 1, 1, 0, 0 .endm .macro SAVE_C_REGS_EXCEPT_RCX_R891011 - SAVE_C_REGS_HELPER 0, 1, 0, 0 + SAVE_C_REGS_HELPER 0, 1, 0, 0, 0 + .endm + .macro SAVE_C_REGS_EXCEPT_RAX_RCX_R11 + SAVE_C_REGS_HELPER 0, 0, 0, 1, 0 .endm .macro SAVE_EXTRA_REGS offset=0 @@ -179,6 +184,9 @@ For 32-bit we have the following conventions - kernel is built with .macro RESTORE_C_REGS_EXCEPT_R11 RESTORE_C_REGS_HELPER 1,1,0,1,1 .endm + .macro RESTORE_C_REGS_EXCEPT_RCX_R11 + RESTORE_C_REGS_HELPER 1,0,0,1,1 + .endm .macro RESTORE_RSI_RDI RESTORE_C_REGS_HELPER 0,0,0,0,0 .endm diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 54737e5..2091e2e 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -121,14 +121,12 @@ ENDPROC(native_usergs_sysret64) #endif /* - * C code is not supposed to know about undefined top of stack. Every time - * a C function with an pt_regs argument is called from the SYSCALL based - * fast path FIXUP_TOP_OF_STACK is needed. + * C code is not supposed to know that the iret frame is not populated. + * Every time a C function with an pt_regs argument is called from + * the SYSCALL based fast path FIXUP_TOP_OF_STACK is needed. * RESTORE_TOP_OF_STACK syncs the syscall state after any possible ptregs * manipulation. */ - - /* %rsp:at FRAMEEND */ .macro FIXUP_TOP_OF_STACK tmp offset=0 movq PER_CPU_VAR(old_rsp),\tmp movq \tmp,RSP+\offset(%rsp) @@ -136,15 +134,13 @@ ENDPROC(native_usergs_sysret64) movq $__USER_CS,CS+\offset(%rsp) movq RIP+\offset(%rsp),\tmp /* get rip */ movq \tmp,RCX+\offset(%rsp) /* copy it to rcx as sysret would do */ - movq R11+\offset(%rsp),\tmp /* get eflags */ - movq \tmp,EFLAGS+\offset(%rsp) + movq EFLAGS+\offset(%rsp),\tmp /* ditto for rflags->r11 */ + movq \tmp,R11+\offset(%rsp) .endm .macro RESTORE_TOP_OF_STACK tmp offset=0 movq RSP+\offset(%rsp),\tmp movq \tmp,PER_CPU_VAR(old_rsp) - movq EFLAGS+\offset(%rsp),\tmp - movq \tmp,R11+\offset(%rsp) .endm /* @@ -257,9 +253,10 @@ GLOBAL(system_call_after_swapgs) */ ENABLE_INTERRUPTS(CLBR_NONE) ALLOC_PT_GPREGS_ON_STACK 6*8 /* 6*8: space for orig_ax and iret frame */ - SAVE_C_REGS_EXCEPT_RAX_RCX + SAVE_C_REGS_EXCEPT_RAX_RCX_R11 movq $-ENOSYS,RAX(%rsp) movq_cfi rax,ORIG_RAX + movq %r11,EFLAGS(%rsp) movq %rcx,RIP(%rsp) CFI_REL_OFFSET rip,RIP testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,SIZEOF_PTREGS) @@ -277,7 +274,7 @@ system_call_fastpath: movq %rax,RAX(%rsp) /* * Syscall return path ending with SYSRET (fast path) - * Has incomplete stack frame and undefined top of stack. + * Has incompletely filled pt_regs, iret frame is also incomplete. */ ret_from_sys_call: testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,SIZEOF_PTREGS) @@ -291,9 +288,10 @@ ret_from_sys_call: * sysretq will re-enable interrupts: */ TRACE_IRQS_ON - RESTORE_C_REGS_EXCEPT_RCX - movq RIP(%rsp),%rcx + RESTORE_C_REGS_EXCEPT_RCX_R11 + movq RIP(%rsp),%rcx CFI_REGISTER rip,rcx + movq EFLAGS(%rsp),%r11 /*CFI_REGISTER rflags,r11*/ movq PER_CPU_VAR(old_rsp), %rsp /* @@ -422,22 +420,9 @@ ENTRY(stub_\func) END(stub_\func) .endm - .macro FIXED_FRAME label,func -ENTRY(\label) - CFI_STARTPROC - DEFAULT_FRAME 0, 8 /* offset 8: return address */ - FIXUP_TOP_OF_STACK %r11, 8 - call \func - RESTORE_TOP_OF_STACK %r11, 8 - ret - CFI_ENDPROC -END(\label) - .endm - FORK_LIKE clone FORK_LIKE fork FORK_LIKE vfork - FIXED_FRAME stub_iopl, sys_iopl ENTRY(stub_execve) CFI_STARTPROC diff --git a/arch/x86/syscalls/syscall_64.tbl b/arch/x86/syscalls/syscall_64.tbl index 8d656fb..9ef32d5 100644 --- a/arch/x86/syscalls/syscall_64.tbl +++ b/arch/x86/syscalls/syscall_64.tbl @@ -178,7 +178,7 @@ 169 common reboot sys_reboot 170 common sethostname sys_sethostname 171 common setdomainname sys_setdomainname -172 common iopl stub_iopl +172 common iopl sys_iopl 173 common ioperm sys_ioperm 174 64 create_module 175 common init_module sys_init_module diff --git a/arch/x86/um/sys_call_table_64.c b/arch/x86/um/sys_call_table_64.c index 5cdfa9d..a75d8700 100644 --- a/arch/x86/um/sys_call_table_64.c +++ b/arch/x86/um/sys_call_table_64.c @@ -16,7 +16,7 @@ */ /* Not going to be implemented by UML, since we have no hardware. */ -#define stub_iopl sys_ni_syscall +#define sys_iopl sys_ni_syscall #define sys_ioperm sys_ni_syscall /* -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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