commit 7fa0da5373685e7ed249af3fa317ab1e1ba8b0a6 upstream.
The hypercall page is no longer needed. It can be removed, as from the
Xen perspective it is optional.
But, from Linux's perspective, it removes naked RET instructions that
escape the speculative protections that Call Depth Tracking and/or
Untrain Ret are trying to achieve.
This is part of XSA-466 / CVE-2024-53241.
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit b4845bb6383821a9516ce30af3a27dc873e37fd4 upstream.
Add generic hypercall functions usable for all normal (i.e. not iret)
hypercalls. Depending on the guest type and the processor vendor
different functions need to be used due to the to be used instruction
for entering the hypervisor:
- PV guests need to use syscall
- HVM/PVH guests on Intel need to use vmcall
- HVM/PVH guests on AMD and Hygon need to use vmmcall
As PVH guests need to issue hypercalls very early during boot, there
is a 4th hypercall function needed for HVM/PVH which can be used on
Intel and AMD processors. It will check the vendor type and then set
the Intel or AMD specific function to use via static_call().
This is part of XSA-466 / CVE-2024-53241.
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Co-developed-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit a2796dff62d6c6bfc5fbebdf2bee0d5ac0438906 upstream.
Instead of jumping to the Xen hypercall page for doing the iret
hypercall, directly code the required sequence in xen-asm.S.
This is done in preparation of no longer using hypercall page at all,
as it has shown to cause problems with speculation mitigations.
This is part of XSA-466 / CVE-2024-53241.
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ Upstream commit fac1bceeeb04886fc2ee952672e6e6c85ce41dca ]
When running as a Xen PV dom0 the kernel is loaded by the hypervisor
using a different memory map than that of the host. In order to
minimize the required changes in the kernel, the kernel adapts its
memory map to that of the host. In order to do that it is checking
for conflicts of its load address with the host memory map.
Unfortunately the tested memory range does not include the .brk
area, which might result in crashes or memory corruption when this
area does conflict with the memory map of the host.
Fix the test by using the _end label instead of __bss_stop.
Fixes: 808fdb71936c ("xen: check for kernel memory conflicting with memory layout")
Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
commit afd30525a659ac0ae0904f0cb4a2ca75522c3123 upstream.
USERGS_SYSRET64 is used to return from a syscall via SYSRET, but
a Xen PV guest will nevertheless use the IRET hypercall, as there
is no sysret PV hypercall defined.
So instead of testing all the prerequisites for doing a sysret and
then mangling the stack for Xen PV again for doing an iret just use
the iret exit from the beginning.
This can easily be done via an ALTERNATIVE like it is done for the
sysenter compat case already.
It should be noted that this drops the optimization in Xen for not
restoring a few registers when returning to user mode, but it seems
as if the saved instructions in the kernel more than compensate for
this drop (a kernel build in a Xen PV guest was slightly faster with
this patch applied).
While at it remove the stale sysret32 remnants.
[ pawan: Brad Spengler and Salvatore Bonaccorso <carnil@debian.org>
reported a problem with the 5.10 backport commit edc702b4a820
("x86/entry_64: Add VERW just before userspace transition").
When CONFIG_PARAVIRT_XXL=y, CLEAR_CPU_BUFFERS is not executed in
syscall_return_via_sysret path as USERGS_SYSRET64 is runtime
patched to:
.cpu_usergs_sysret64 = { 0x0f, 0x01, 0xf8,
0x48, 0x0f, 0x07 }, // swapgs; sysretq
which is missing CLEAR_CPU_BUFFERS. It turns out dropping
USERGS_SYSRET64 simplifies the code, allowing CLEAR_CPU_BUFFERS
to be explicitly added to syscall_return_via_sysret path. Below
is with CONFIG_PARAVIRT_XXL=y and this patch applied:
syscall_return_via_sysret:
...
<+342>: swapgs
<+345>: xchg %ax,%ax
<+347>: verw -0x1a2(%rip) <------
<+354>: sysretq
]
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Link: https://lkml.kernel.org/r/20210120135555.32594-6-jgross@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ Upstream commit 3fb0fdb3bbe7aed495109b3296b06c2409734023 ]
On 32-bit kernels, the stackprotector canary is quite nasty -- it is
stored at %gs:(20), which is nasty because 32-bit kernels use %fs for
percpu storage. It's even nastier because it means that whether %gs
contains userspace state or kernel state while running kernel code
depends on whether stackprotector is enabled (this is
CONFIG_X86_32_LAZY_GS), and this setting radically changes the way
that segment selectors work. Supporting both variants is a
maintenance and testing mess.
Merely rearranging so that percpu and the stack canary
share the same segment would be messy as the 32-bit percpu address
layout isn't currently compatible with putting a variable at a fixed
offset.
Fortunately, GCC 8.1 added options that allow the stack canary to be
accessed as %fs:__stack_chk_guard, effectively turning it into an ordinary
percpu variable. This lets us get rid of all of the code to manage the
stack canary GDT descriptor and the CONFIG_X86_32_LAZY_GS mess.
(That name is special. We could use any symbol we want for the
%fs-relative mode, but for CONFIG_SMP=n, gcc refuses to let us use any
name other than __stack_chk_guard.)
Forcibly disable stackprotector on older compilers that don't support
the new options and turn the stack canary into a percpu variable. The
"lazy GS" approach is now used for all 32-bit configurations.
Also makes load_gs_index() work on 32-bit kernels. On 64-bit kernels,
it loads the GS selector and updates the user GSBASE accordingly. (This
is unchanged.) On 32-bit kernels, it loads the GS selector and updates
GSBASE, which is now always the user base. This means that the overall
effect is the same on 32-bit and 64-bit, which avoids some ifdeffery.
[ bp: Massage commit message. ]
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/c0ff7dba14041c7e5d1cae5d4df052f03759bef3.1613243844.git.luto@kernel.org
Stable-dep-of: e3f269ed0acc ("x86/pm: Work around false positive kmemleak report in msr_build_context()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ Upstream commit 3693bb4465e6e32a204a5b86d3ec7e6b9f7e67c2 ]
kasprintf() returns a pointer to dynamically allocated memory
which can be NULL upon failure. Ensure the allocation was successful
by checking the pointer validity.
Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202401161119.iof6BQsf-lkp@intel.com/
Suggested-by: Markus Elfring <Markus.Elfring@web.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20240119094948.275390-1-chentao@kylinos.cn
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
