AcoSail/kernel_optimize_test
8
0
Fork 0
forked from luck/tmp_suning_uos_patched
Code Pull Requests Activity

x86/xen: Add xenpv_restore_regs_and_return_to_usermode()

Browse Source 
[ Upstream commit 5c8f6a2e316efebb3ba93d8c1af258155dcf5632 ]

In the native case, PER_CPU_VAR(cpu_tss_rw + TSS_sp0) is the
trampoline stack. But XEN pv doesn't use trampoline stack, so
PER_CPU_VAR(cpu_tss_rw + TSS_sp0) is also the kernel stack.

In that case, source and destination stacks are identical, which means
that reusing swapgs_restore_regs_and_return_to_usermode() in XEN pv
would cause %rsp to move up to the top of the kernel stack and leave the
IRET frame below %rsp.

This is dangerous as it can be corrupted if #NMI / #MC hit as either of
these events occurring in the middle of the stack pushing would clobber
data on the (original) stack.

And, with  XEN pv, swapgs_restore_regs_and_return_to_usermode() pushing
the IRET frame on to the original address is useless and error-prone
when there is any future attempt to modify the code.

 [ bp: Massage commit message. ]

Fixes: 7f2590a110 ("x86/entry/64: Use a per-CPU trampoline stack for IDT entries")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lkml.kernel.org/r/20211126101209.8613-4-jiangshanlai@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Lai Jiangshan 2021-11-26 18:11:23 +08:00 committed by Greg Kroah-Hartman
parent 8b9279cad2
commit 2015ffa3a4
2 changed files with 24 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/x86/entry/entry_64.S
View File

@ -575,6 +575,10 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
ud2
1:
#endif
#ifdef CONFIG_XEN_PV
ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
#endif
POP_REGS pop_rdi=0
/*

20
arch/x86/xen/xen-asm.S
View File

@ -19,6 +19,7 @@
#include <linux/init.h>
#include <linux/linkage.h>
#include <../entry/calling.h>
/*
* Enable events. This clears the event mask and tests the pending
@ -235,6 +236,25 @@ SYM_CODE_START(xen_sysret64)
jmp hypercall_iret
SYM_CODE_END(xen_sysret64)
/*
* XEN pv doesn't use trampoline stack, PER_CPU_VAR(cpu_tss_rw + TSS_sp0) is
* also the kernel stack. Reusing swapgs_restore_regs_and_return_to_usermode()
* in XEN pv would cause %rsp to move up to the top of the kernel stack and
* leave the IRET frame below %rsp, which is dangerous to be corrupted if #NMI
* interrupts. And swapgs_restore_regs_and_return_to_usermode() pushing the IRET
* frame at the same address is useless.
*/
SYM_CODE_START(xenpv_restore_regs_and_return_to_usermode)
UNWIND_HINT_REGS
POP_REGS
/* stackleak_erase() can work safely on the kernel stack. */
STACKLEAK_ERASE_NOCLOBBER
addq $8, %rsp /* skip regs->orig_ax */
jmp xen_iret
SYM_CODE_END(xenpv_restore_regs_and_return_to_usermode)
/*
* Xen handles syscall callbacks much like ordinary exceptions, which
* means we have: