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    Subject[PATCH 5.10 138/148] x86/kvm: fix FASTOP_SIZE when return thunks are enabled
    Date
    From: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

    commit 84e7051c0bc1f2a13101553959b3a9d9a8e24939 upstream.

    The return thunk call makes the fastop functions larger, just like IBT
    does. Consider a 16-byte FASTOP_SIZE when CONFIG_RETHUNK is enabled.

    Otherwise, functions will be incorrectly aligned and when computing their
    position for differently sized operators, they will executed in the middle
    or end of a function, which may as well be an int3, leading to a crash
    like:

    [ 36.091116] int3: 0000 [#1] SMP NOPTI
    [ 36.091119] CPU: 3 PID: 1371 Comm: qemu-system-x86 Not tainted 5.15.0-41-generic #44
    [ 36.091120] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
    [ 36.091121] RIP: 0010:xaddw_ax_dx+0x9/0x10 [kvm]
    [ 36.091185] Code: 00 0f bb d0 c3 cc cc cc cc 48 0f bb d0 c3 cc cc cc cc 0f 1f 80 00 00 00 00 0f c0 d0 c3 cc cc cc cc 66 0f c1 d0 c3 cc cc cc cc <0f> 1f 80 00 00 00 00 0f c1 d0 c3 cc cc cc cc 48 0f c1 d0 c3 cc cc
    [ 36.091186] RSP: 0018:ffffb1f541143c98 EFLAGS: 00000202
    [ 36.091188] RAX: 0000000089abcdef RBX: 0000000000000001 RCX: 0000000000000000
    [ 36.091188] RDX: 0000000076543210 RSI: ffffffffc073c6d0 RDI: 0000000000000200
    [ 36.091189] RBP: ffffb1f541143ca0 R08: ffff9f1803350a70 R09: 0000000000000002
    [ 36.091190] R10: ffff9f1803350a70 R11: 0000000000000000 R12: ffff9f1803350a70
    [ 36.091190] R13: ffffffffc077fee0 R14: 0000000000000000 R15: 0000000000000000
    [ 36.091191] FS: 00007efdfce8d640(0000) GS:ffff9f187dd80000(0000) knlGS:0000000000000000
    [ 36.091192] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    [ 36.091192] CR2: 0000000000000000 CR3: 0000000009b62002 CR4: 0000000000772ee0
    [ 36.091195] PKRU: 55555554
    [ 36.091195] Call Trace:
    [ 36.091197] <TASK>
    [ 36.091198] ? fastop+0x5a/0xa0 [kvm]
    [ 36.091222] x86_emulate_insn+0x7b8/0xe90 [kvm]
    [ 36.091244] x86_emulate_instruction+0x2f4/0x630 [kvm]
    [ 36.091263] ? kvm_arch_vcpu_load+0x7c/0x230 [kvm]
    [ 36.091283] ? vmx_prepare_switch_to_host+0xf7/0x190 [kvm_intel]
    [ 36.091290] complete_emulated_mmio+0x297/0x320 [kvm]
    [ 36.091310] kvm_arch_vcpu_ioctl_run+0x32f/0x550 [kvm]
    [ 36.091330] kvm_vcpu_ioctl+0x29e/0x6d0 [kvm]
    [ 36.091344] ? kvm_vcpu_ioctl+0x120/0x6d0 [kvm]
    [ 36.091357] ? __fget_files+0x86/0xc0
    [ 36.091362] ? __fget_files+0x86/0xc0
    [ 36.091363] __x64_sys_ioctl+0x92/0xd0
    [ 36.091366] do_syscall_64+0x59/0xc0
    [ 36.091369] ? syscall_exit_to_user_mode+0x27/0x50
    [ 36.091370] ? do_syscall_64+0x69/0xc0
    [ 36.091371] ? syscall_exit_to_user_mode+0x27/0x50
    [ 36.091372] ? __x64_sys_writev+0x1c/0x30
    [ 36.091374] ? do_syscall_64+0x69/0xc0
    [ 36.091374] ? exit_to_user_mode_prepare+0x37/0xb0
    [ 36.091378] ? syscall_exit_to_user_mode+0x27/0x50
    [ 36.091379] ? do_syscall_64+0x69/0xc0
    [ 36.091379] ? do_syscall_64+0x69/0xc0
    [ 36.091380] ? do_syscall_64+0x69/0xc0
    [ 36.091381] ? do_syscall_64+0x69/0xc0
    [ 36.091381] entry_SYSCALL_64_after_hwframe+0x61/0xcb
    [ 36.091384] RIP: 0033:0x7efdfe6d1aff
    [ 36.091390] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <41> 89 c0 3d 00 f0 ff ff 77 1f 48 8b 44 24 18 64 48 2b 04 25 28 00
    [ 36.091391] RSP: 002b:00007efdfce8c460 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
    [ 36.091393] RAX: ffffffffffffffda RBX: 000000000000ae80 RCX: 00007efdfe6d1aff
    [ 36.091393] RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 000000000000000c
    [ 36.091394] RBP: 0000558f1609e220 R08: 0000558f13fb8190 R09: 00000000ffffffff
    [ 36.091394] R10: 0000558f16b5e950 R11: 0000000000000246 R12: 0000000000000000
    [ 36.091394] R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000000
    [ 36.091396] </TASK>
    [ 36.091397] Modules linked in: isofs nls_iso8859_1 kvm_intel joydev kvm input_leds serio_raw sch_fq_codel dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua ipmi_devintf ipmi_msghandler drm msr ip_tables x_tables autofs4 btrfs blake2b_generic zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel virtio_net net_failover crypto_simd ahci xhci_pci cryptd psmouse virtio_blk libahci xhci_pci_renesas failover
    [ 36.123271] ---[ end trace db3c0ab5a48fabcc ]---
    [ 36.123272] RIP: 0010:xaddw_ax_dx+0x9/0x10 [kvm]
    [ 36.123319] Code: 00 0f bb d0 c3 cc cc cc cc 48 0f bb d0 c3 cc cc cc cc 0f 1f 80 00 00 00 00 0f c0 d0 c3 cc cc cc cc 66 0f c1 d0 c3 cc cc cc cc <0f> 1f 80 00 00 00 00 0f c1 d0 c3 cc cc cc cc 48 0f c1 d0 c3 cc cc
    [ 36.123320] RSP: 0018:ffffb1f541143c98 EFLAGS: 00000202
    [ 36.123321] RAX: 0000000089abcdef RBX: 0000000000000001 RCX: 0000000000000000
    [ 36.123321] RDX: 0000000076543210 RSI: ffffffffc073c6d0 RDI: 0000000000000200
    [ 36.123322] RBP: ffffb1f541143ca0 R08: ffff9f1803350a70 R09: 0000000000000002
    [ 36.123322] R10: ffff9f1803350a70 R11: 0000000000000000 R12: ffff9f1803350a70
    [ 36.123323] R13: ffffffffc077fee0 R14: 0000000000000000 R15: 0000000000000000
    [ 36.123323] FS: 00007efdfce8d640(0000) GS:ffff9f187dd80000(0000) knlGS:0000000000000000
    [ 36.123324] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    [ 36.123325] CR2: 0000000000000000 CR3: 0000000009b62002 CR4: 0000000000772ee0
    [ 36.123327] PKRU: 55555554
    [ 36.123328] Kernel panic - not syncing: Fatal exception in interrupt
    [ 36.123410] Kernel Offset: 0x1400000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
    [ 36.135305] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

    Fixes: aa3d480315ba ("x86: Use return-thunk in asm code")
    Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
    Co-developed-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Borislav Petkov <bp@suse.de>
    Cc: Josh Poimboeuf <jpoimboe@kernel.org>
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
    Message-Id: <20220713171241.184026-1-cascardo@canonical.com>
    Tested-by: Jack Wang <jinpu.wang@ionos.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/kvm/emulate.c | 10 ++++++----
    1 file changed, 6 insertions(+), 4 deletions(-)

    --- a/arch/x86/kvm/emulate.c
    +++ b/arch/x86/kvm/emulate.c
    @@ -188,8 +188,12 @@
    #define X8(x...) X4(x), X4(x)
    #define X16(x...) X8(x), X8(x)

    -#define NR_FASTOP (ilog2(sizeof(ulong)) + 1)
    -#define FASTOP_SIZE 8
    +#define NR_FASTOP (ilog2(sizeof(ulong)) + 1)
    +#define RET_LENGTH (1 + (4 * IS_ENABLED(CONFIG_RETHUNK)) + \
    + IS_ENABLED(CONFIG_SLS))
    +#define FASTOP_LENGTH (ENDBR_INSN_SIZE + 7 + RET_LENGTH)
    +#define FASTOP_SIZE (8 << ((FASTOP_LENGTH > 8) & 1) << ((FASTOP_LENGTH > 16) & 1))
    +static_assert(FASTOP_LENGTH <= FASTOP_SIZE);

    struct opcode {
    u64 flags : 56;
    @@ -438,8 +442,6 @@ static int fastop(struct x86_emulate_ctx
    * RET | JMP __x86_return_thunk [1,5 bytes; CONFIG_RETHUNK]
    * INT3 [1 byte; CONFIG_SLS]
    */
    -#define RET_LENGTH (1 + (4 * IS_ENABLED(CONFIG_RETHUNK)) + \
    - IS_ENABLED(CONFIG_SLS))
    #define SETCC_LENGTH (3 + RET_LENGTH)
    #define SETCC_ALIGN (4 << ((SETCC_LENGTH > 4) & 1) << ((SETCC_LENGTH > 8) & 1))
    static_assert(SETCC_LENGTH <= SETCC_ALIGN);

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