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Date: Sat, 4 Apr 2015 20:55:19 +0200
From: Denys Vlasenko <dvlasenk@...hat.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Denys Vlasenko <dvlasenk@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Steven Rostedt <rostedt@...dmis.org>,
Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...capital.net>,
Oleg Nesterov <oleg@...hat.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Alexei Starovoitov <ast@...mgrid.com>,
Will Drewry <wad@...omium.org>,
Kees Cook <keescook@...omium.org>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH] x86: clear EXTRA_REGS for all executable formats
On failure, sys_execve does not clobber EXTRA_REGS, so we can just
return to userpsace without saving/restoring them.
On success, ELF_PLAT_INIT in sys_execve clears all these registers.
On other executable formats:
binfmt_flat.c has similar FLAT_PLAT_INIT, but x86 (and everyone else
except sh) doesn't define it.
binfmt_elf_fdpic.c has ELF_FDPIC_PLAT_INIT, but x86 (and most others)
doesn't define it.
There are no such hooks in binfmt_aout.c et al. We inherit
EXTRA_REGS from the prior executable.
This was not intended.
This change removes SAVE/RESTORE_EXTRA_REGS in stub_execve,
removes register clearing in ELF_PLAT_INIT,
and instead simply clears them on success in stub_execve.
Run-tested.
Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Ingo Molnar <mingo@...nel.org>
CC: Borislav Petkov <bp@...en8.de>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Andy Lutomirski <luto@...capital.net>
CC: Oleg Nesterov <oleg@...hat.com>
CC: Frederic Weisbecker <fweisbec@...il.com>
CC: Alexei Starovoitov <ast@...mgrid.com>
CC: Will Drewry <wad@...omium.org>
CC: Kees Cook <keescook@...omium.org>
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.org
---
arch/x86/include/asm/calling.h | 9 ++++++++
arch/x86/include/asm/elf.h | 7 +++---
arch/x86/kernel/entry_64.S | 50 +++++++++++++++++++-----------------------
3 files changed, 35 insertions(+), 31 deletions(-)
diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h
index 4b5f7bf..1c8b50e 100644
--- a/arch/x86/include/asm/calling.h
+++ b/arch/x86/include/asm/calling.h
@@ -151,6 +151,15 @@ For 32-bit we have the following conventions - kernel is built with
movq_cfi_restore 5*8+\offset, rbx
.endm
+ .macro ZERO_EXTRA_REGS
+ xorl %r15d, %r15d
+ xorl %r14d, %r14d
+ xorl %r13d, %r13d
+ xorl %r12d, %r12d
+ xorl %ebp, %ebp
+ xorl %ebx, %ebx
+ .endm
+
.macro RESTORE_C_REGS_HELPER rstor_rax=1, rstor_rcx=1, rstor_r11=1, rstor_r8910=1, rstor_rdx=1
.if \rstor_r11
movq_cfi_restore 6*8, r11
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index bd292ce..935588d9 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -171,10 +171,11 @@ do { \
static inline void elf_common_init(struct thread_struct *t,
struct pt_regs *regs, const u16 ds)
{
- regs->ax = regs->bx = regs->cx = regs->dx = 0;
- regs->si = regs->di = regs->bp = 0;
+ /* Commented-out registers are cleared in stub_execve */
+ /*regs->ax = regs->bx =*/ regs->cx = regs->dx = 0;
+ regs->si = regs->di /*= regs->bp*/ = 0;
regs->r8 = regs->r9 = regs->r10 = regs->r11 = 0;
- regs->r12 = regs->r13 = regs->r14 = regs->r15 = 0;
+ /*regs->r12 = regs->r13 = regs->r14 = regs->r15 = 0;*/
t->fs = t->gs = 0;
t->fsindex = t->gsindex = 0;
t->ds = t->es = ds;
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 13185c5..65485b3 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -419,25 +419,27 @@ END(stub_\func)
ENTRY(stub_execve)
CFI_STARTPROC
- addq $8, %rsp
- DEFAULT_FRAME 0
- SAVE_EXTRA_REGS
- call sys_execve
- movq %rax,RAX(%rsp)
- RESTORE_EXTRA_REGS
- jmp int_ret_from_sys_call
+ DEFAULT_FRAME 0, 8
+ call sys_execve
+return_from_execve:
+ testl %eax, %eax
+ jz 1f
+ /* exec failed, can use fast SYSRET code path in this case */
+ ret
+1:
+ /* must use IRET code path (pt_regs->cs may have changed) */
+ addq $8, %rsp
+ ZERO_EXTRA_REGS
+ movq %rax,RAX(%rsp)
+ jmp int_ret_from_sys_call
CFI_ENDPROC
END(stub_execve)
ENTRY(stub_execveat)
CFI_STARTPROC
- addq $8, %rsp
- DEFAULT_FRAME 0
- SAVE_EXTRA_REGS
- call sys_execveat
- movq %rax,RAX(%rsp)
- RESTORE_EXTRA_REGS
- jmp int_ret_from_sys_call
+ DEFAULT_FRAME 0, 8
+ call sys_execveat
+ jmp return_from_execve
CFI_ENDPROC
END(stub_execveat)
@@ -472,25 +474,17 @@ END(stub_x32_rt_sigreturn)
ENTRY(stub_x32_execve)
CFI_STARTPROC
- addq $8, %rsp
- DEFAULT_FRAME 0
- SAVE_EXTRA_REGS
- call compat_sys_execve
- movq %rax,RAX(%rsp)
- RESTORE_EXTRA_REGS
- jmp int_ret_from_sys_call
+ DEFAULT_FRAME 0, 8
+ call compat_sys_execve
+ jmp return_from_execve
CFI_ENDPROC
END(stub_x32_execve)
ENTRY(stub_x32_execveat)
CFI_STARTPROC
- addq $8, %rsp
- DEFAULT_FRAME 0
- SAVE_EXTRA_REGS
- call compat_sys_execveat
- movq %rax,RAX(%rsp)
- RESTORE_EXTRA_REGS
- jmp int_ret_from_sys_call
+ DEFAULT_FRAME 0, 8
+ call compat_sys_execveat
+ jmp return_from_execve
CFI_ENDPROC
END(stub_x32_execveat)
--
1.8.1.4
--
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