kernel.git/arch/x86/kernel/process.c, branch linux-5.6.y

x86/speculation: Prevent rogue cross-process SSBD shutdown

2020-06-17T14:41:54Z

commit dbbe2ad02e9df26e372f38cc3e70dab9222c832e upstream. On context switch the change of TIF_SSBD and TIF_SPEC_IB are evaluated to adjust the mitigations accordingly. This is optimized to avoid the expensive MSR write if not needed. This optimization is buggy and allows an attacker to shutdown the SSBD protection of a victim process. The update logic reads the cached base value for the speculation control MSR which has neither the SSBD nor the STIBP bit set. It then OR's the SSBD bit only when TIF_SSBD is different and requests the MSR update. That means if TIF_SSBD of the previous and next task are the same, then the base value is not updated, even if TIF_SSBD is set. The MSR write is not requested. Subsequently if the TIF_STIBP bit differs then the STIBP bit is updated in the base value and the MSR is written with a wrong SSBD value. This was introduced when the per task/process conditional STIPB switching was added on top of the existing SSBD switching. It is exploitable if the attacker creates a process which enforces SSBD and has the contrary value of STIBP than the victim process (i.e. if the victim process enforces STIBP, the attacker process must not enforce it; if the victim process does not enforce STIBP, the attacker process must enforce it) and schedule it on the same core as the victim process. If the victim runs after the attacker the victim becomes vulnerable to Spectre V4. To fix this, update the MSR value independent of the TIF_SSBD difference and dependent on the SSBD mitigation method available. This ensures that a subsequent STIPB initiated MSR write has the correct state of SSBD. [ tglx: Handle X86_FEATURE_VIRT_SSBD & X86_FEATURE_VIRT_SSBD correctly and massaged changelog ] Fixes: 5bfbe3ad5840 ("x86/speculation: Prepare for per task indirect branch speculation control") Signed-off-by: Anthony Steinhauser Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman

x86/ioperm: Prevent a memory leak when fork fails

2020-06-03T06:23:34Z

commit 4bfe6cce133cad82cea04490c308795275857782 upstream. In the copy_process() routine called by _do_fork(), failure to allocate a PID (or further along in the function) will trigger an invocation to exit_thread(). This is done to clean up from an earlier call to copy_thread_tls(). Naturally, the child task is passed into exit_thread(), however during the process, io_bitmap_exit() nullifies the parent's io_bitmap rather than the child's. As copy_thread_tls() has been called ahead of the failure, the reference count on the calling thread's io_bitmap is incremented as we would expect. However, io_bitmap_exit() doesn't accept any arguments, and thus assumes it should trash the current thread's io_bitmap reference rather than the child's. This is pretty sneaky in practice, because in all instances but this one, exit_thread() is called with respect to the current task and everything works out. A determined attacker can issue an appropriate ioctl (i.e. KDENABIO) to get a bitmap allocated, and force a clone3() syscall to fail by passing in a zeroed clone_args structure. The kernel handles the erroneous struct and the buggy code path is followed, and even though the parent's reference to the io_bitmap is trashed, the child still holds a reference and thus the structure will never be freed. Fix this by tweaking io_bitmap_exit() and its subroutines to accept a task_struct argument which to operate on. Fixes: ea5f1cd7ab49 ("x86/ioperm: Remove bitmap if all permissions dropped") Signed-off-by: Jay Lang Signed-off-by: Thomas Gleixner Cc: stable#@vger.kernel.org Link: https://lkml.kernel.org/r/20200524162742.253727-1-jaytlang@mit.edu Signed-off-by: Greg Kroah-Hartman

x86/ioperm: Add new paravirt function update_io_bitmap()

2020-02-29T11:43:09Z

Commit 111e7b15cf10f6 ("x86/ioperm: Extend IOPL config to control ioperm() as well") reworked the iopl syscall to use I/O bitmaps. Unfortunately this broke Xen PV domains using that syscall as there is currently no I/O bitmap support in PV domains. Add I/O bitmap support via a new paravirt function update_io_bitmap which Xen PV domains can use to update their I/O bitmaps via a hypercall. Fixes: 111e7b15cf10f6 ("x86/ioperm: Extend IOPL config to control ioperm() as well") Reported-by: Jan Beulich Signed-off-by: Juergen Gross Signed-off-by: Thomas Gleixner Tested-by: Jan Beulich Reviewed-by: Jan Beulich Cc: # 5.5 Link: https://lkml.kernel.org/r/20200218154712.25490-1-jgross@suse.com

x86/process: Remove set but not used variables prev and next

2019-12-14T07:26:00Z

Remove two unused variables: arch/x86/kernel/process.c: In function ‘__switch_to_xtra’: arch/x86/kernel/process.c:618:31: warning: variable ‘next’ set but not used [-Wunused-but-set-variable] 618 | struct thread_struct *prev, *next; | ^~~~ arch/x86/kernel/process.c:618:24: warning: variable ‘prev’ set but not used [-Wunused-but-set-variable] 618 | struct thread_struct *prev, *next; | They are never used and so can be removed. Signed-off-by: yu kuai Signed-off-by: Borislav Petkov Cc: Andy Lutomirski Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Thomas Gleixner Cc: x86-ml Cc: yi.zhang@huawei.com Cc: zhengbin13@huawei.com Link: https://lkml.kernel.org/r/20191213121253.10072-1-yukuai3@huawei.com

x86/ioperm: Save an indentation level in tss_update_io_bitmap()

2019-11-30T17:06:56Z

... for better readability. No functional changes. [ Minor edit. ] Signed-off-by: Borislav Petkov Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/ioperm: Fix use of deprecated config option

2019-11-20T22:40:05Z

The commit 111e7b15cf10 ("x86/ioperm: Extend IOPL config to control ioperm() as well") replaced X86_IOPL_EMULATION with X86_IOPL_IOPERM. However it appears that there was at least one spot missed as tss_update_io_bitmap() still had a reference to it contained in the code. The result of this is that it exposed a NULL pointer dereference as seen below with a linux-next next-20191120 kernel: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] SMP PTI CPU: 5 PID: 1542 Comm: ovs-vswitchd Tainted: G W 5.4.0-rc8-next-20191120 #125 RIP: 0010:tss_update_io_bitmap+0x4e/0x180 Code: 10 31 c0 65 48 03 1d 69 54 5d 6d 65 48 8b 04 25 40 8c 01 00 48 8b 10 \ f7 c2 00 00 40 00 0f 84 8c 00 00 00 4c 8b a0 c0 22 00 00 <49> 8b 04 \ 24 48 39 43 68 74 2e 8b 53 70 41 39 54 24 0c 48 8d 7b 78 RSP: 0018:ffffb8888a0ebf08 EFLAGS: 00010006 RAX: ffff8a429811a680 RBX: ffff8a4c3f946000 RCX: 0000000000000011 RDX: 0000000000400080 RSI: 0000000000400080 RDI: 0000000000000000 RBP: ffffb8888a0ebf30 R08: 00007ffffb5d7ce0 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 FS: 00007f68a9635c40(0000) GS:ffff8a4c3f940000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 000000103572a001 CR4: 00000000001606e0 Call Trace: ? syscall_slow_exit_work+0x39/0xdb do_syscall_64+0x1a5/0x200 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7f68a7aff797 Fixes: 111e7b15cf10 ("x86/ioperm: Extend IOPL config to control ioperm() as well") Signed-off-by: Alexander Duyck Signed-off-by: Borislav Petkov Reviewed-by: Thomas Gleixner Cc: "H. Peter Anvin" Cc: Andy Lutomirski Cc: Ingo Molnar Cc: Rik van Riel Cc: x86-ml Link: https://lkml.kernel.org/r/20191120222426.3060.18462.stgit@localhost.localdomain

x86/ioperm: Extend IOPL config to control ioperm() as well

2019-11-16T10:24:06Z

If iopl() is disabled, then providing ioperm() does not make much sense. Rename the config option and disable/enable both syscalls with it. Guard the code with #ifdefs where appropriate. Suggested-by: Andy Lutomirski Signed-off-by: Thomas Gleixner

x86/iopl: Restrict iopl() permission scope

2019-11-16T10:24:05Z

The access to the full I/O port range can be also provided by the TSS I/O bitmap, but that would require to copy 8k of data on scheduling in the task. As shown with the sched out optimization TSS.io_bitmap_base can be used to switch the incoming task to a preallocated I/O bitmap which has all bits zero, i.e. allows access to all I/O ports. Implementing this allows to provide an iopl() emulation mode which restricts the IOPL level 3 permissions to I/O port access but removes the STI/CLI permission which is coming with the hardware IOPL mechansim. Provide a config option to switch IOPL to emulation mode, make it the default and while at it also provide an option to disable IOPL completely. Signed-off-by: Thomas Gleixner Acked-by: Andy Lutomirski

x86/ioperm: Share I/O bitmap if identical

2019-11-16T10:24:04Z

The I/O bitmap is duplicated on fork. That's wasting memory and slows down fork. There is no point to do so. As long as the bitmap is not modified it can be shared between threads and processes. Add a refcount and just share it on fork. If a task modifies the bitmap then it has to do the duplication if and only if it is shared. Signed-off-by: Thomas Gleixner Acked-by: Andy Lutomirski

x86/ioperm: Remove bitmap if all permissions dropped

2019-11-16T10:24:03Z

If ioperm() results in a bitmap with all bits set (no permissions to any I/O port), then handling that bitmap on context switch and exit to user mode is pointless. Drop it. Move the bitmap exit handling to the ioport code and reuse it for both the thread exit path and dropping it. This allows to reuse this code for the upcoming iopl() emulation. Signed-off-by: Thomas Gleixner Acked-by: Andy Lutomirski