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x86/vdso/32: Save extra registers in the INT80 vsyscall path

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The goal is to integrate the SYSENTER and SYSCALL32 entry paths
with the INT80 path.  SYSENTER clobbers ESP and EIP.  SYSCALL32
clobbers ECX (and, invisibly, R11).  SYSRETL (long mode to
compat mode) clobbers ECX and, invisibly, R11.  SYSEXIT (which
we only need for native 32-bit) clobbers ECX and EDX.

This means that we'll need to provide ESP to the kernel in a
register (I chose ECX, since it's only needed for SYSENTER) and
we need to provide the args that normally live in ECX and EDX in
memory.

The epilogue needs to restore ECX and EDX, since user code
relies on regs being preserved.

We don't need to do anything special about EIP, since the kernel
already knows where we are.  The kernel will eventually need to
know where int $0x80 lands, so add a vdso_image entry for it.

The only user-visible effect of this code is that ptrace-induced
changes to ECX and EDX during fast syscalls will be lost.  This
is already the case for the SYSENTER path.

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/b860925adbee2d2627a0671fbfe23a7fd04127f8.1444091584.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2015-10-05 17:48:01 -07:00 committed by Ingo Molnar
parent 7bcdea4d05
commit 8242c6c84a
3 changed files with 26 additions and 1 deletions
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1
arch/x86/entry/vdso/vdso2c.c
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@ -101,6 +101,7 @@ struct vdso_sym required_syms[] = {
{"__kernel_vsyscall", true},
{"__kernel_sigreturn", true},
{"__kernel_rt_sigreturn", true},
{"int80_landing_pad", true},
};
__attribute__((format(printf, 1, 2))) __attribute__((noreturn))

25
arch/x86/entry/vdso/vdso32/system_call.S
View File

@ -16,7 +16,30 @@
ALIGN
__kernel_vsyscall:
CFI_STARTPROC
int $0x80
/*
* Reshuffle regs so that all of any of the entry instructions
* will preserve enough state.
*/
pushl %edx
CFI_ADJUST_CFA_OFFSET 4
CFI_REL_OFFSET edx, 0
pushl %ecx
CFI_ADJUST_CFA_OFFSET 4
CFI_REL_OFFSET ecx, 0
movl %esp, %ecx
/* Enter using int $0x80 */
movl (%esp), %ecx
int $0x80
GLOBAL(int80_landing_pad)
/* Restore ECX and EDX in case they were clobbered. */
popl %ecx
CFI_RESTORE ecx
CFI_ADJUST_CFA_OFFSET -4
popl %edx
CFI_RESTORE edx
CFI_ADJUST_CFA_OFFSET -4
ret
CFI_ENDPROC

1
arch/x86/include/asm/vdso.h
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@ -26,6 +26,7 @@ struct vdso_image {
long sym___kernel_sigreturn;
long sym___kernel_rt_sigreturn;
long sym___kernel_vsyscall;
long sym_int80_landing_pad;
};
#ifdef CONFIG_X86_64