6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jinghao Jia jinghao7@illinois.edu
commit f5d03da48d062966c94f0199d20be0b3a37a7982 upstream.
kprobe_emulate_call_indirect currently uses int3_emulate_call to emulate indirect calls. However, int3_emulate_call always assumes the size of the call to be 5 bytes when calculating the return address. This is incorrect for register-based indirect calls in x86, which can be either 2 or 3 bytes depending on whether REX prefix is used. At kprobe runtime, the incorrect return address causes control flow to land onto the wrong place after return -- possibly not a valid instruction boundary. This can lead to a panic like the following:
[ 7.308204][ C1] BUG: unable to handle page fault for address: 000000000002b4d8 [ 7.308883][ C1] #PF: supervisor read access in kernel mode [ 7.309168][ C1] #PF: error_code(0x0000) - not-present page [ 7.309461][ C1] PGD 0 P4D 0 [ 7.309652][ C1] Oops: 0000 [#1] SMP [ 7.309929][ C1] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.7.0-rc5-trace-for-next #6 [ 7.310397][ C1] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-20220807_005459-localhost 04/01/2014 [ 7.311068][ C1] RIP: 0010:__common_interrupt+0x52/0xc0 [ 7.311349][ C1] Code: 01 00 4d 85 f6 74 39 49 81 fe 00 f0 ff ff 77 30 4c 89 f7 4d 8b 5e 68 41 ba 91 76 d8 42 45 03 53 fc 74 02 0f 0b cc ff d3 65 48 <8b> 05 30 c7 ff 7e 65 4c 89 3d 28 c7 ff 7e 5b 41 5c 41 5e 41 5f c3 [ 7.312512][ C1] RSP: 0018:ffffc900000e0fd0 EFLAGS: 00010046 [ 7.312899][ C1] RAX: 0000000000000001 RBX: 0000000000000023 RCX: 0000000000000001 [ 7.313334][ C1] RDX: 00000000000003cd RSI: 0000000000000001 RDI: ffff888100d302a4 [ 7.313702][ C1] RBP: 0000000000000001 R08: 0ef439818636191f R09: b1621ff338a3b482 [ 7.314146][ C1] R10: ffffffff81e5127b R11: ffffffff81059810 R12: 0000000000000023 [ 7.314509][ C1] R13: 0000000000000000 R14: ffff888100d30200 R15: 0000000000000000 [ 7.314951][ C1] FS: 0000000000000000(0000) GS:ffff88813bc80000(0000) knlGS:0000000000000000 [ 7.315396][ C1] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 7.315691][ C1] CR2: 000000000002b4d8 CR3: 0000000003028003 CR4: 0000000000370ef0 [ 7.316153][ C1] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 7.316508][ C1] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 7.316948][ C1] Call Trace: [ 7.317123][ C1] <IRQ> [ 7.317279][ C1] ? __die_body+0x64/0xb0 [ 7.317482][ C1] ? page_fault_oops+0x248/0x370 [ 7.317712][ C1] ? __wake_up+0x96/0xb0 [ 7.317964][ C1] ? exc_page_fault+0x62/0x130 [ 7.318211][ C1] ? asm_exc_page_fault+0x22/0x30 [ 7.318444][ C1] ? __cfi_native_send_call_func_single_ipi+0x10/0x10 [ 7.318860][ C1] ? default_idle+0xb/0x10 [ 7.319063][ C1] ? __common_interrupt+0x52/0xc0 [ 7.319330][ C1] common_interrupt+0x78/0x90 [ 7.319546][ C1] </IRQ> [ 7.319679][ C1] <TASK> [ 7.319854][ C1] asm_common_interrupt+0x22/0x40 [ 7.320082][ C1] RIP: 0010:default_idle+0xb/0x10 [ 7.320309][ C1] Code: 4c 01 c7 4c 29 c2 e9 72 ff ff ff cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 b8 0c 67 40 a5 66 90 0f 00 2d 09 b9 3b 00 fb f4 <fa> c3 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 b8 0c 67 40 a5 e9 [ 7.321449][ C1] RSP: 0018:ffffc9000009bee8 EFLAGS: 00000256 [ 7.321808][ C1] RAX: ffff88813bca8b68 RBX: 0000000000000001 RCX: 000000000001ef0c [ 7.322227][ C1] RDX: 0000000000000000 RSI: 0000000000000001 RDI: 000000000001ef0c [ 7.322656][ C1] RBP: ffffc9000009bef8 R08: 8000000000000000 R09: 00000000000008c2 [ 7.323083][ C1] R10: 0000000000000000 R11: ffffffff81058e70 R12: 0000000000000000 [ 7.323530][ C1] R13: ffff8881002b30c0 R14: 0000000000000000 R15: 0000000000000000 [ 7.323948][ C1] ? __cfi_lapic_next_deadline+0x10/0x10 [ 7.324239][ C1] default_idle_call+0x31/0x50 [ 7.324464][ C1] do_idle+0xd3/0x240 [ 7.324690][ C1] cpu_startup_entry+0x25/0x30 [ 7.324983][ C1] start_secondary+0xb4/0xc0 [ 7.325217][ C1] secondary_startup_64_no_verify+0x179/0x17b [ 7.325498][ C1] </TASK> [ 7.325641][ C1] Modules linked in: [ 7.325906][ C1] CR2: 000000000002b4d8 [ 7.326104][ C1] ---[ end trace 0000000000000000 ]--- [ 7.326354][ C1] RIP: 0010:__common_interrupt+0x52/0xc0 [ 7.326614][ C1] Code: 01 00 4d 85 f6 74 39 49 81 fe 00 f0 ff ff 77 30 4c 89 f7 4d 8b 5e 68 41 ba 91 76 d8 42 45 03 53 fc 74 02 0f 0b cc ff d3 65 48 <8b> 05 30 c7 ff 7e 65 4c 89 3d 28 c7 ff 7e 5b 41 5c 41 5e 41 5f c3 [ 7.327570][ C1] RSP: 0018:ffffc900000e0fd0 EFLAGS: 00010046 [ 7.327910][ C1] RAX: 0000000000000001 RBX: 0000000000000023 RCX: 0000000000000001 [ 7.328273][ C1] RDX: 00000000000003cd RSI: 0000000000000001 RDI: ffff888100d302a4 [ 7.328632][ C1] RBP: 0000000000000001 R08: 0ef439818636191f R09: b1621ff338a3b482 [ 7.329223][ C1] R10: ffffffff81e5127b R11: ffffffff81059810 R12: 0000000000000023 [ 7.329780][ C1] R13: 0000000000000000 R14: ffff888100d30200 R15: 0000000000000000 [ 7.330193][ C1] FS: 0000000000000000(0000) GS:ffff88813bc80000(0000) knlGS:0000000000000000 [ 7.330632][ C1] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 7.331050][ C1] CR2: 000000000002b4d8 CR3: 0000000003028003 CR4: 0000000000370ef0 [ 7.331454][ C1] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 7.331854][ C1] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 7.332236][ C1] Kernel panic - not syncing: Fatal exception in interrupt [ 7.332730][ C1] Kernel Offset: disabled [ 7.333044][ C1] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---
The relevant assembly code is (from objdump, faulting address highlighted):
ffffffff8102ed9d: 41 ff d3 call *%r11 ffffffff8102eda0: 65 48 <8b> 05 30 c7 ff mov %gs:0x7effc730(%rip),%rax
The emulation incorrectly sets the return address to be ffffffff8102ed9d + 0x5 = ffffffff8102eda2, which is the 8b byte in the middle of the next mov. This in turn causes incorrect subsequent instruction decoding and eventually triggers the page fault above.
Instead of invoking int3_emulate_call, perform push and jmp emulation directly in kprobe_emulate_call_indirect. At this point we can obtain the instruction size from p->ainsn.size so that we can calculate the correct return address.
Link: https://lore.kernel.org/all/20240102233345.385475-1-jinghao7@illinois.edu/
Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Cc: stable@vger.kernel.org Signed-off-by: Jinghao Jia jinghao7@illinois.edu Signed-off-by: Masami Hiramatsu (Google) mhiramat@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/kprobes/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -576,7 +576,8 @@ static void kprobe_emulate_call_indirect { unsigned long offs = addrmode_regoffs[p->ainsn.indirect.reg];
- int3_emulate_call(regs, regs_get_register(regs, offs)); + int3_emulate_push(regs, regs->ip - INT3_INSN_SIZE + p->ainsn.size); + int3_emulate_jmp(regs, regs_get_register(regs, offs)); } NOKPROBE_SYMBOL(kprobe_emulate_call_indirect);