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Date: Wed, 24 Aug 2011 14:44:19 +0200 From: Borislav Petkov <bp@...64.org> To: Al Viro <viro@...IV.linux.org.uk> CC: Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Lutomirski <luto@....edu>, "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...64.org>, Ingo Molnar <mingo@...nel.org>, "user-mode-linux-devel@...ts.sourceforge.net" <user-mode-linux-devel@...ts.sourceforge.net>, Richard Weinberger <richard@....at>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "mingo@...hat.com" <mingo@...hat.com> Subject: [PATCH] x86, asm: Document some of the syscall asm glue On Tue, Aug 23, 2011 at 06:33:17PM +0100, Al Viro wrote: > * asm glue is subtle, evil and doesn't have anywhere near enough > documentation ;-/ I took the liberty to document some of your asm glue analysis in an attempt to make the code a bit more understandable. How about the following: -- From: Borislav Petkov <borislav.petkov@....com> Date: Wed, 24 Aug 2011 14:30:43 +0200 Subject: [PATCH] x86, asm: Document some of the syscall asm glue Document some of the asm glue around compat SYSCALL32 and do a whitespace cleanup while at it. See linked thread below for further reference. Link: http://lkml.kernel.org/r/20110820011845.GC2203@ZenIV.linux.org.uk Signed-off-by: Borislav Petkov <borislav.petkov@....com> --- arch/x86/ia32/ia32entry.S | 138 ++++++++++++++++++++++++++----------------- arch/x86/kernel/entry_64.S | 19 +++++- 2 files changed, 98 insertions(+), 59 deletions(-) diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S index a0e866d..8254432 100644 --- a/arch/x86/ia32/ia32entry.S +++ b/arch/x86/ia32/ia32entry.S @@ -1,16 +1,16 @@ /* - * Compatibility mode system call entry point for x86-64. - * + * Compatibility mode system call entry point for x86-64. + * * Copyright 2000-2002 Andi Kleen, SuSE Labs. - */ + */ #include <asm/dwarf2.h> #include <asm/calling.h> #include <asm/asm-offsets.h> #include <asm/current.h> #include <asm/errno.h> -#include <asm/ia32_unistd.h> -#include <asm/thread_info.h> +#include <asm/ia32_unistd.h> +#include <asm/thread_info.h> #include <asm/segment.h> #include <asm/irqflags.h> #include <linux/linkage.h> @@ -38,11 +38,11 @@ xchg %ecx,%esi movl %ebx,%edi movl %edx,%edx /* zero extension */ - .endm + .endm - /* clobbers %eax */ + /* clobbers %eax */ .macro CLEAR_RREGS offset=0, _r9=rax - xorl %eax,%eax + xorl %eax,%eax movq %rax,\offset+R11(%rsp) movq %rax,\offset+R10(%rsp) movq %\_r9,\offset+R9(%rsp) @@ -69,7 +69,7 @@ movl \offset+64(%rsp),%edi movl %eax,%eax /* zero extension */ .endm - + .macro CFI_STARTPROC32 simple CFI_STARTPROC \simple CFI_UNDEFINED r8 @@ -106,14 +106,14 @@ ENDPROC(native_irq_enable_sysexit) * %esi Arg4 * %edi Arg5 * %ebp user stack - * 0(%ebp) Arg6 - * + * 0(%ebp) Arg6 + * * Interrupts off. - * + * * This is purely a fast path. For anything complicated we use the int 0x80 * path below. Set up a complete hardware stack frame to share code * with the int 0x80 path. - */ + */ ENTRY(ia32_sysenter_target) CFI_STARTPROC32 simple CFI_SIGNAL_FRAME @@ -127,7 +127,7 @@ ENTRY(ia32_sysenter_target) * disabled irqs, here we enable it straight after entry: */ ENABLE_INTERRUPTS(CLBR_NONE) - movl %ebp,%ebp /* zero extension */ + movl %ebp,%ebp /* zero extension */ pushq_cfi $__USER32_DS /*CFI_REL_OFFSET ss,0*/ pushq_cfi %rbp @@ -144,12 +144,12 @@ ENTRY(ia32_sysenter_target) pushq_cfi %rax cld SAVE_ARGS 0,1,0 - /* no need to do an access_ok check here because rbp has been - 32bit zero extended */ + /* no need to do an access_ok check here because rbp has been + 32bit zero extended */ 1: movl (%rbp),%ebp - .section __ex_table,"a" - .quad 1b,ia32_badarg - .previous + .section __ex_table,"a" + .quad 1b,ia32_badarg + .previous GET_THREAD_INFO(%r10) orl $TS_COMPAT,TI_status(%r10) testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%r10) @@ -170,7 +170,7 @@ sysenter_dispatch: sysexit_from_sys_call: andl $~TS_COMPAT,TI_status(%r10) /* clear IF, that popfq doesn't enable interrupts early */ - andl $~0x200,EFLAGS-R11(%rsp) + andl $~0x200,EFLAGS-R11(%rsp) movl RIP-R11(%rsp),%edx /* User %eip */ CFI_REGISTER rip,rdx RESTORE_ARGS 0,24,0,0,0,0 @@ -260,20 +260,21 @@ ENDPROC(ia32_sysenter_target) * Arguments: * %eax System call number. * %ebx Arg1 - * %ecx return EIP + * %ecx return EIP * %edx Arg3 * %esi Arg4 * %edi Arg5 - * %ebp Arg2 [note: not saved in the stack frame, should not be touched] - * %esp user stack + * %ebp Arg2 [note: not saved in the stack frame, should not be touched + * because it is callee-saved in 64-bit calling convention] + * %esp user stack * 0(%esp) Arg6 - * + * * Interrupts off. - * + * * This is purely a fast path. For anything complicated we use the int 0x80 * path below. Set up a complete hardware stack frame to share code - * with the int 0x80 path. - */ + * with the int 0x80 path. + */ ENTRY(ia32_cstar_target) CFI_STARTPROC32 simple CFI_SIGNAL_FRAME @@ -281,34 +282,57 @@ ENTRY(ia32_cstar_target) CFI_REGISTER rip,rcx /*CFI_REGISTER rflags,r11*/ SWAPGS_UNSAFE_STACK + + /* stash away usermode stack ptr */ movl %esp,%r8d CFI_REGISTER rsp,r8 movq PER_CPU_VAR(kernel_stack),%rsp + /* * No need to follow this irqs on/off section: the syscall * disabled irqs and here we enable it straight after entry: */ ENABLE_INTERRUPTS(CLBR_NONE) SAVE_ARGS 8,0,0 - movl %eax,%eax /* zero extension */ + movl %eax,%eax /* zero extension */ movq %rax,ORIG_RAX-ARGOFFSET(%rsp) + + /* return-RIP is in %ecx when executing SYSCALL */ movq %rcx,RIP-ARGOFFSET(%rsp) CFI_REL_OFFSET rip,RIP-ARGOFFSET - movq %rbp,RCX-ARGOFFSET(%rsp) /* this lies slightly to ptrace */ + + /* + * Put Arg2 into %rcx pt_regs slot to match kernel syscall + * calling conventions, i.e. what INT80 would expect; + * this lies slightly to ptrace + */ + movq %rbp,RCX-ARGOFFSET(%rsp) movl %ebp,%ecx movq $__USER32_CS,CS-ARGOFFSET(%rsp) movq $__USER32_DS,SS-ARGOFFSET(%rsp) + + /* rFLAGS is in %r11 when executing SYSCALL */ movq %r11,EFLAGS-ARGOFFSET(%rsp) /*CFI_REL_OFFSET rflags,EFLAGS-ARGOFFSET*/ - movq %r8,RSP-ARGOFFSET(%rsp) + + /* save usermode stack ptr into pt_regs */ + movq %r8,RSP-ARGOFFSET(%rsp) CFI_REL_OFFSET rsp,RSP-ARGOFFSET - /* no need to do an access_ok check here because r8 has been - 32bit zero extended */ - /* hardware stack frame is complete now */ + + /* + * Get Arg6 which is on the usermode stack; no need to do an + * access_ok check here because %r8 has been 32bit zero extended. + * hardware stack frame is complete now. + */ 1: movl (%r8),%r9d + + /* + * handle pagefaulting when accessing usermode stack by returning + * -EFAULT + */ .section __ex_table,"a" .quad 1b,ia32_badarg - .previous + .previous GET_THREAD_INFO(%r10) orl $TS_COMPAT,TI_status(%r10) testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%r10) @@ -331,7 +355,7 @@ sysretl_from_sys_call: RESTORE_ARGS 0,-ARG_SKIP,0,0,0 movl RIP-ARGOFFSET(%rsp),%ecx CFI_REGISTER rip,rcx - movl EFLAGS-ARGOFFSET(%rsp),%r11d + movl EFLAGS-ARGOFFSET(%rsp),%r11d /*CFI_REGISTER rflags,r11*/ xorq %r10,%r10 xorq %r9,%r9 @@ -340,7 +364,7 @@ sysretl_from_sys_call: movl RSP-ARGOFFSET(%rsp),%esp CFI_RESTORE rsp USERGS_SYSRET32 - + #ifdef CONFIG_AUDITSYSCALL cstar_auditsys: CFI_RESTORE_STATE @@ -358,6 +382,8 @@ cstar_tracesys: testl $(_TIF_WORK_SYSCALL_ENTRY & ~_TIF_SYSCALL_AUDIT),TI_flags(%r10) jz cstar_auditsys #endif + + /* put Arg6 into %ebp where ptrace expects it */ xchgl %r9d,%ebp SAVE_REST CLEAR_RREGS 0, r9 @@ -366,21 +392,23 @@ cstar_tracesys: call syscall_trace_enter LOAD_ARGS32 ARGOFFSET, 1 /* reload args from stack in case ptrace changed it */ RESTORE_REST + + /* sync back Arg6's possibly changed value where it is expected by C */ xchgl %ebp,%r9d cmpq $(IA32_NR_syscalls-1),%rax ja int_ret_from_sys_call /* cstar_tracesys has set RAX(%rsp) */ jmp cstar_do_call END(ia32_cstar_target) - + ia32_badarg: movq $-EFAULT,%rax jmp ia32_sysret CFI_ENDPROC -/* - * Emulated IA32 system calls via int 0x80. +/* + * Emulated IA32 system calls via int 0x80. * - * Arguments: + * Arguments: * %eax System call number. * %ebx Arg1 * %ecx Arg2 @@ -390,13 +418,13 @@ ia32_badarg: * %ebp Arg6 [note: not saved in the stack frame, should not be touched] * * Notes: - * Uses the same stack frame as the x86-64 version. + * Uses the same stack frame as the x86-64 version. * All registers except %eax must be saved (but ptrace may violate that) * Arguments are zero extended. For system calls that want sign extension and * take long arguments a wrapper is needed. Most calls can just be called * directly. - * Assumes it is only called from user space and entered with interrupts off. - */ + * Assumes it is only called from user space and entered with interrupts off. + */ ENTRY(ia32_syscall) CFI_STARTPROC32 simple @@ -433,9 +461,9 @@ ia32_sysret: movq %rax,RAX-ARGOFFSET(%rsp) ia32_ret_from_sys_call: CLEAR_RREGS -ARGOFFSET - jmp int_ret_from_sys_call + jmp int_ret_from_sys_call -ia32_tracesys: +ia32_tracesys: SAVE_REST CLEAR_RREGS movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */ @@ -457,13 +485,13 @@ quiet_ni_syscall: movq $-ENOSYS,%rax ret CFI_ENDPROC - + .macro PTREGSCALL label, func, arg .globl \label \label: leaq \func(%rip),%rax leaq -ARGOFFSET+8(%rsp),\arg /* 8 for return address */ - jmp ia32_ptregs_common + jmp ia32_ptregs_common .endm CFI_STARTPROC32 @@ -537,7 +565,7 @@ ia32_sys_call_table: .quad quiet_ni_syscall /* old stty syscall holder */ .quad quiet_ni_syscall /* old gtty syscall holder */ .quad sys_access - .quad sys_nice + .quad sys_nice .quad quiet_ni_syscall /* 35 */ /* old ftime syscall holder */ .quad sys_sync .quad sys32_kill @@ -616,7 +644,7 @@ ia32_sys_call_table: .quad stub32_iopl /* 110 */ .quad sys_vhangup .quad quiet_ni_syscall /* old "idle" system call */ - .quad sys32_vm86_warning /* vm86old */ + .quad sys32_vm86_warning /* vm86old */ .quad compat_sys_wait4 .quad sys_swapoff /* 115 */ .quad compat_sys_sysinfo @@ -669,7 +697,7 @@ ia32_sys_call_table: .quad sys_mremap .quad sys_setresuid16 .quad sys_getresuid16 /* 165 */ - .quad sys32_vm86_warning /* vm86 */ + .quad sys32_vm86_warning /* vm86 */ .quad quiet_ni_syscall /* query_module */ .quad sys_poll .quad compat_sys_nfsservctl @@ -724,10 +752,10 @@ ia32_sys_call_table: .quad sys_mincore .quad sys_madvise .quad compat_sys_getdents64 /* 220 getdents64 */ - .quad compat_sys_fcntl64 + .quad compat_sys_fcntl64 .quad quiet_ni_syscall /* tux */ - .quad quiet_ni_syscall /* security */ - .quad sys_gettid + .quad quiet_ni_syscall /* security */ + .quad sys_gettid .quad sys32_readahead /* 225 */ .quad sys_setxattr .quad sys_lsetxattr @@ -742,7 +770,7 @@ ia32_sys_call_table: .quad sys_lremovexattr .quad sys_fremovexattr .quad sys_tkill - .quad sys_sendfile64 + .quad sys_sendfile64 .quad compat_sys_futex /* 240 */ .quad compat_sys_sched_setaffinity .quad compat_sys_sched_getaffinity @@ -754,7 +782,7 @@ ia32_sys_call_table: .quad compat_sys_io_submit .quad sys_io_cancel .quad sys32_fadvise64 /* 250 */ - .quad quiet_ni_syscall /* free_huge_pages */ + .quad quiet_ni_syscall /* free_huge_pages */ .quad sys_exit_group .quad sys32_lookup_dcookie .quad sys_epoll_create diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 6419bb0..9569f11 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -607,10 +607,16 @@ tracesys: GLOBAL(int_ret_from_sys_call) DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF + + /* + * check the Requestor Privilege Level of the CS selector + * previously pushed on the stack. If 0, we're returning + * to kernel space. + */ testl $3,CS-ARGOFFSET(%rsp) je retint_restore_args - movl $_TIF_ALLWORK_MASK,%edi /* edi: mask to check */ + movl $_TIF_ALLWORK_MASK,%edi GLOBAL(int_with_check) LOCKDEP_SYS_EXIT_IRQ GET_THREAD_INFO(%rcx) @@ -618,11 +624,16 @@ GLOBAL(int_with_check) andl %edi,%edx jnz int_careful andl $~TS_COMPAT,TI_status(%rcx) + + /* no work pending, return to userspace */ jmp retint_swapgs - /* Either reschedule or signal or syscall exit tracking needed. */ - /* First do a reschedule test. */ - /* edx: work, edi: workmask */ + /* + * Either reschedule or signal or syscall exit tracking + * needed. First do a reschedule test. + * + * edx: work, edi: workmask + */ int_careful: bt $TIF_NEED_RESCHED,%edx jnc int_very_careful -- 1.7.4 -- Regards/Gruss, Boris. Advanced Micro Devices GmbH Einsteinring 24, 85609 Dornach GM: Alberto Bozzo Reg: Dornach, Landkreis Muenchen HRB Nr. 43632 WEEE Registernr: 129 19551 -- 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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