linux/tools/testing/selftests/x86/thunks.S
Andy Lutomirski e22438f8e9 x86, selftests: Add a test for the "sysret_ss_attrs" bug
On AMD CPUs, SYSRET can return with a valid SS descriptor with
with the hidden attributes set to an unusable state.  Make sure
the kernel doesn't let this happen.  This detects an
as-yet-unfixed regression.

Note that the 64-bit version of this test fails on AMD CPUs on
all kernel versions, although the issue in the 64-bit case is
much less severe than in the 32-bit case.

Reported-by: Brian Gerst <brgerst@gmail.com>
Tested-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Tests: e7d6eefaaa ("x86/vdso32/syscall.S: Do not load __USER32_DS to %ss")
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/resend_4d740841bac383742949e2fefb03982736595087.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-05-08 13:33:59 +02:00

68 lines
1.3 KiB
ArmAsm

/*
* thunks.S - assembly helpers for mixed-bitness code
* Copyright (c) 2015 Andrew Lutomirski
*
* This program is free software; you can redistribute it and/or modify
* it under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* These are little helpers that make it easier to switch bitness on
* the fly.
*/
.text
.global call32_from_64
.type call32_from_64, @function
call32_from_64:
// rdi: stack to use
// esi: function to call
// Save registers
pushq %rbx
pushq %rbp
pushq %r12
pushq %r13
pushq %r14
pushq %r15
pushfq
// Switch stacks
mov %rsp,(%rdi)
mov %rdi,%rsp
// Switch to compatibility mode
pushq $0x23 /* USER32_CS */
pushq $1f
lretq
1:
.code32
// Call the function
call *%esi
// Switch back to long mode
jmp $0x33,$1f
.code64
1:
// Restore the stack
mov (%rsp),%rsp
// Restore registers
popfq
popq %r15
popq %r14
popq %r13
popq %r12
popq %rbp
popq %rbx
ret
.size call32_from_64, .-call32_from_64