Commit-ID: 8242c6c84a644e5f0f721e4ae2bd542f640c89f9 Gitweb: http://git.kernel.org/tip/8242c6c84a644e5f0f721e4ae2bd542f640c89f9 Author: Andy Lutomirski <[email protected]> AuthorDate: Mon, 5 Oct 2015 17:48:01 -0700 Committer: Ingo Molnar <[email protected]> CommitDate: Fri, 9 Oct 2015 09:41:06 +0200
x86/vdso/32: Save extra registers in the INT80 vsyscall path 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 <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Link: http://lkml.kernel.org/r/b860925adbee2d2627a0671fbfe23a7fd04127f8.1444091584.git.l...@kernel.org Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/entry/vdso/vdso2c.c | 1 + arch/x86/entry/vdso/vdso32/system_call.S | 25 ++++++++++++++++++++++++- arch/x86/include/asm/vdso.h | 1 + 3 files changed, 26 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/vdso/vdso2c.c b/arch/x86/entry/vdso/vdso2c.c index 2637eb1..785d992 100644 --- a/arch/x86/entry/vdso/vdso2c.c +++ b/arch/x86/entry/vdso/vdso2c.c @@ -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)) diff --git a/arch/x86/entry/vdso/vdso32/system_call.S b/arch/x86/entry/vdso/vdso32/system_call.S index b52cbfb..d591fe9 100644 --- a/arch/x86/entry/vdso/vdso32/system_call.S +++ b/arch/x86/entry/vdso/vdso32/system_call.S @@ -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 diff --git a/arch/x86/include/asm/vdso.h b/arch/x86/include/asm/vdso.h index 5bcb1de..756de91 100644 --- a/arch/x86/include/asm/vdso.h +++ b/arch/x86/include/asm/vdso.h @@ -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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
