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x86/vdso/compat: Wire up SYSENTER and SYSCSALL for compat userspace
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What, you didn't realize that SYSENTER and SYSCALL were actually
the same thing? :)

Unlike the old code, this actually passes the ptrace_syscall_32
test on AMD systems.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/b74615af58d785aa02d917213ec64e2022a2c796.1444091585.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Andy Lutomirski authored and Ingo Molnar committed Oct 9, 2015
1 parent 710246d commit a474e67
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Showing 2 changed files with 62 additions and 36 deletions.
90 changes: 54 additions & 36 deletions arch/x86/entry/entry_64_compat.S
View file
Original file line number Diff line number Diff line change
Expand Up @@ -52,15 +52,18 @@ ENTRY(entry_SYSENTER_compat)
SWAPGS_UNSAFE_STACK
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp

/* Zero-extending 32-bit regs, do not remove */
movl %ebp, %ebp
/*
* User tracing code (ptrace or signal handlers) might assume that
* the saved RAX contains a 32-bit number when we're invoking a 32-bit
* syscall. Just in case the high bits are nonzero, zero-extend
* the syscall number. (This could almost certainly be deleted
* with no ill effects.)
*/
movl %eax, %eax

movl ASM_THREAD_INFO(TI_sysenter_return, %rsp, 0), %r10d

/* Construct struct pt_regs on stack */
pushq $__USER32_DS /* pt_regs->ss */
pushq %rbp /* pt_regs->sp */
pushq %rcx /* pt_regs->sp */

/*
* Push flags. This is nasty. First, interrupts are currently
Expand All @@ -70,17 +73,28 @@ ENTRY(entry_SYSENTER_compat)
*/
pushfq /* pt_regs->flags (except IF = 0) */
orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */
ASM_CLAC /* Clear AC after saving FLAGS */

pushq $__USER32_CS /* pt_regs->cs */
pushq %r10 /* pt_regs->ip = thread_info->sysenter_return */
xorq %r8,%r8
pushq %r8 /* pt_regs->ip = 0 (placeholder) */
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq %rcx /* pt_regs->cx (will be overwritten) */
pushq $-ENOSYS /* pt_regs->ax */
pushq %r8 /* pt_regs->r8 = 0 */
pushq %r8 /* pt_regs->r9 = 0 */
pushq %r8 /* pt_regs->r10 = 0 */
pushq %r8 /* pt_regs->r11 = 0 */
pushq %rbx /* pt_regs->rbx */
pushq %rbp /* pt_regs->rbp */
pushq %r8 /* pt_regs->r12 = 0 */
pushq %r8 /* pt_regs->r13 = 0 */
pushq %r8 /* pt_regs->r14 = 0 */
pushq %r8 /* pt_regs->r15 = 0 */
cld
sub $(10*8), %rsp /* pt_regs->r8-11, bp, bx, r12-15 not saved */

/*
* Sysenter doesn't filter flags, so we need to clear NT
Expand All @@ -93,16 +107,15 @@ ENTRY(entry_SYSENTER_compat)
jnz sysenter_fix_flags
sysenter_flags_fixed:

/* Temporary: SYSENTER is disabled. */
#ifdef CONFIG_CONTEXT_TRACKING
call enter_from_user_mode
#endif
ENABLE_INTERRUPTS(CLBR_NONE)
movl $11, %edi
call do_exit
/*
* User mode is traced as though IRQs are on, and SYSENTER
* turned them off.
*/
TRACE_IRQS_OFF

/* Unreachable. */
ud2
movq %rsp, %rdi
call do_fast_syscall_32
jmp .Lsyscall_32_done

sysenter_fix_flags:
pushq $X86_EFLAGS_FIXED
Expand Down Expand Up @@ -135,26 +148,14 @@ ENDPROC(entry_SYSENTER_compat)
* edi arg5
* esp user stack
* 0(%esp) arg6
*
* This is purely a fast path. For anything complicated we use the int 0x80
* path below. We set up a complete hardware stack frame to share code
* with the int 0x80 path.
*/
ENTRY(entry_SYSCALL_compat)
/*
* Interrupts are off on entry.
* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
* it is too small to ever cause noticeable irq latency.
*/
/* Interrupts are off on entry. */
SWAPGS_UNSAFE_STACK

/* Temporary: SYSCALL32 is disabled. */
movl $-ENOSYS, %eax
USERGS_SYSRET32

/* Stash user ESP and switch to the kernel stack. */
movl %esp, %r8d
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
ENABLE_INTERRUPTS(CLBR_NONE)

/* Zero-extending 32-bit regs, do not remove */
movl %eax, %eax
Expand All @@ -169,13 +170,29 @@ ENTRY(entry_SYSCALL_compat)
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */
pushq %rbp /* pt_regs->cx */
movl %ebp, %ecx
pushq %rcx /* pt_regs->cx (will be overwritten) */
pushq $-ENOSYS /* pt_regs->ax */
sub $(10*8), %rsp /* pt_regs->r8-11, bp, bx, r12-15 not saved */
xorq %r8,%r8
pushq %r8 /* pt_regs->r8 = 0 */
pushq %r8 /* pt_regs->r9 = 0 */
pushq %r8 /* pt_regs->r10 = 0 */
pushq %r8 /* pt_regs->r11 = 0 */
pushq %rbx /* pt_regs->rbx */
pushq %rbp /* pt_regs->rbp */
pushq %r8 /* pt_regs->r12 = 0 */
pushq %r8 /* pt_regs->r13 = 0 */
pushq %r8 /* pt_regs->r14 = 0 */
pushq %r8 /* pt_regs->r15 = 0 */

/* Unreachable. */
ud2
/*
* User mode is traced as though IRQs are on, and SYSENTER
* turned them off.
*/
TRACE_IRQS_OFF

movq %rsp, %rdi
call do_fast_syscall_32
jmp .Lsyscall_32_done
END(entry_SYSCALL_compat)

/*
Expand Down Expand Up @@ -243,6 +260,7 @@ ENTRY(entry_INT80_compat)

movq %rsp, %rdi
call do_int80_syscall_32
.Lsyscall_32_done:

/* Go back to user mode. */
TRACE_IRQS_ON
Expand Down
8 changes: 8 additions & 0 deletions arch/x86/entry/vdso/vdso32/system_call.S
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,8 @@
*/

#include <asm/dwarf2.h>
#include <asm/cpufeature.h>
#include <asm/alternative-asm.h>

/*
* First get the common code for the sigreturn entry points.
Expand All @@ -28,6 +30,12 @@ __kernel_vsyscall:
CFI_REL_OFFSET ecx, 0
movl %esp, %ecx

#ifdef CONFIG_X86_64
/* If SYSENTER (Intel) or SYSCALL32 (AMD) is available, use it. */
ALTERNATIVE_2 "", "sysenter", X86_FEATURE_SYSENTER32, \
"syscall", X86_FEATURE_SYSCALL32
#endif

/* Enter using int $0x80 */
movl (%esp), %ecx
int $0x80
Expand Down

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