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Sean Christopherson 4b7c3f6d04 KVM: x86: Make x2APIC ID 100% readonly 
Ignore the userspace provided x2APIC ID when fixing up APIC state for
KVM_SET_LAPIC, i.e. make the x2APIC fully readonly in KVM.  Commit
a92e2543d6 ("KVM: x86: use hardware-compatible format for APIC ID
register"), which added the fixup, didn't intend to allow userspace to
modify the x2APIC ID.  In fact, that commit is when KVM first started
treating the x2APIC ID as readonly, apparently to fix some race:

 static inline u32 kvm_apic_id(struct kvm_lapic *apic)
 {
-       return (kvm_lapic_get_reg(apic, APIC_ID) >> 24) & 0xff;
+       /* To avoid a race between apic_base and following APIC_ID update when
+        * switching to x2apic_mode, the x2apic mode returns initial x2apic id.
+        */
+       if (apic_x2apic_mode(apic))
+               return apic->vcpu->vcpu_id;
+
+       return kvm_lapic_get_reg(apic, APIC_ID) >> 24;
 }

Furthermore, KVM doesn't support delivering interrupts to vCPUs with a
modified x2APIC ID, but KVM *does* return the modified value on a guest
RDMSR and for KVM_GET_LAPIC.  I.e. no remotely sane setup can actually
work with a modified x2APIC ID.

Making the x2APIC ID fully readonly fixes a WARN in KVM's optimized map
calculation, which expects the LDR to align with the x2APIC ID.

  WARNING: CPU: 2 PID: 958 at arch/x86/kvm/lapic.c:331 kvm_recalculate_apic_map+0x609/0xa00 [kvm]
  CPU: 2 PID: 958 Comm: recalc_apic_map Not tainted 6.4.0-rc3-vanilla+ #35
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.2-1-1 04/01/2014
  RIP: 0010:kvm_recalculate_apic_map+0x609/0xa00 [kvm]
  Call Trace:
   <TASK>
   kvm_apic_set_state+0x1cf/0x5b0 [kvm]
   kvm_arch_vcpu_ioctl+0x1806/0x2100 [kvm]
   kvm_vcpu_ioctl+0x663/0x8a0 [kvm]
   __x64_sys_ioctl+0xb8/0xf0
   do_syscall_64+0x56/0x80
   entry_SYSCALL_64_after_hwframe+0x46/0xb0
  RIP: 0033:0x7fade8b9dd6f

Unfortunately, the WARN can still trigger for other CPUs than the current
one by racing against KVM_SET_LAPIC, so remove it completely.

Reported-by: Michal Luczaj <mhal@rbox.co>
Closes: https://lore.kernel.org/all/814baa0c-1eaa-4503-129f-059917365e80@rbox.co
Reported-by: Haoyu Wu <haoyuwu254@gmail.com>
Closes: https://lore.kernel.org/all/20240126161633.62529-1-haoyuwu254@gmail.com
Reported-by: syzbot+545f1326f405db4e1c3e@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000c2a6b9061cbca3c3@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20240802202941.344889-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
History 2024-08-13 12:01:46 -04:00
arch KVM: x86: Make x2APIC ID 100% readonly 2024-08-13 12:01:46 -04:00
block blk-throttle: remove more latency dead-code 2024-07-27 10:33:25 -06:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto crypto: testmgr - generate power-of-2 lengths more often 2024-07-13 11:50:28 +12:00
Documentation KVM/arm64 fixes for 6.11, round #1 2024-08-13 06:06:27 -04:00
drivers Three small fixes for interrupt core and drivers: 2024-08-11 10:07:52 -07:00
fs nfsd-6.11 fixes: 2024-08-10 10:44:21 -07:00
include i2c-for-6.11-rc3 2024-08-10 10:28:52 -07:00
init rust: SHADOW_CALL_STACK is incompatible with Rust 2024-08-01 16:15:03 +01:00
io_uring io_uring/net: don't pick multiple buffers for non-bundle send 2024-08-07 15:20:52 -06:00
ipc sysctl: treewide: constify the ctl_table argument of proc_handlers 2024-07-24 20:59:29 +02:00
kernel Updates for time keeping: 2024-08-11 10:15:34 -07:00
lib minmax: don't use max() in situations that want a C constant expression 2024-07-28 20:23:27 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm 9 hotfixes. 5 are cc:stable, 4 either pertain to post-6.10 material or 2024-08-08 07:32:20 -07:00
net nfsd-6.11 fixes: 2024-08-10 10:44:21 -07:00
rust rust: firmware: fix invalid rustdoc link 2024-07-31 13:24:29 +02:00
samples Driver core changes for 6.11-rc1 2024-07-25 10:42:22 -07:00
scripts syscalls: add back legacy __NR_nfsservctl macro 2024-08-06 08:57:02 +02:00
security apparmor-pr-2024-07-24 PR 2024-07-25 2024-07-27 13:28:39 -07:00
sound ASoC: Fixes for v6.11 2024-08-09 09:58:07 +02:00
tools KVM/arm64 fixes for 6.11, round #1 2024-08-13 06:06:27 -04:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt KVM: guest_memfd: abstract how prepared folios are recorded 2024-07-26 14:46:15 -04:00
.clang-format Docs: Move clang-format from process/ to dev-tools/ 2024-06-26 16:36:00 -06:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: add script and target to generate pacman package 2024-07-22 01:24:22 +09:00
.mailmap mailmap: update entry for David Heidelberg 2024-08-07 18:33:56 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS tracing: Update of MAINTAINERS and CREDITS file 2024-07-18 14:08:42 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS sound fixes for 6.11-rc3 2024-08-09 09:25:30 -07:00
Makefile Linux 6.11-rc3 2024-08-11 14:27:14 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.