From 036c07c0c3b8a57d5c96e1f2aab62da0056f8f21 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Thu, 19 May 2022 11:46:58 -0700 Subject: [PATCH] x86/entry: Fix register corruption in compat syscall A panic was reported in the init process on AMD: Run /sbin/init as init process init[1]: segfault at f7fd5ca0 ip 00000000f7f5bbc7 sp 00000000ffa06aa0 error 7 in libc.so[f7f51000+4e000] Code: 8a 44 24 10 88 41 ff 8b 44 24 10 83 c4 2c 5b 5e 5f 5d c3 53 83 ec 08 8b 5c 24 10 81 fb 00 f0 ff ff 76 0c e8 ba dc ff ff f7 db <89> 18 83 cb ff 83 c4 08 89 d8 5b c3 e8 81 60 ff ff 05 28 84 07 00 Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b CPU: 1 PID: 1 Comm: init Tainted: G W 5.18.0-rc7-next-20220519 #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014 Call Trace: dump_stack_lvl+0x57/0x7d panic+0x10f/0x28d do_exit.cold+0x18/0x48 do_group_exit+0x2e/0xb0 get_signal+0xb6d/0xb80 arch_do_signal_or_restart+0x31/0x760 ? show_opcodes.cold+0x1c/0x21 ? force_sig_fault+0x49/0x70 exit_to_user_mode_prepare+0x131/0x1a0 irqentry_exit_to_user_mode+0x5/0x30 asm_exc_page_fault+0x27/0x30 RIP: 0023:0xf7f5bbc7 Code: 8a 44 24 10 88 41 ff 8b 44 24 10 83 c4 2c 5b 5e 5f 5d c3 53 83 ec 08 8b 5c 24 10 81 fb 00 f0 ff ff 76 0c e8 ba dc ff ff f7 db <89> 18 83 cb ff 83 c4 08 89 d8 5b c3 e8 81 60 ff ff 05 28 84 07 00 RSP: 002b:00000000ffa06aa0 EFLAGS: 00000217 RAX: 00000000f7fd5ca0 RBX: 000000000000000c RCX: 0000000000001000 RDX: 0000000000000001 RSI: 00000000f7fd5b60 RDI: 00000000f7fd5b60 RBP: 00000000f7fd1c1c R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 The task's CX register got corrupted by commit 8c42819b61b8 ("x86/entry: Use PUSH_AND_CLEAR_REGS for compat"), which overlooked the fact that compat SYSCALL apparently stores the user's CX value in BP. Before that commit, CX was saved from its stashed value in BP: pushq %rbp /* pt_regs->cx (stashed in bp) */ But then it got changed to: pushq %rcx /* pt_regs->cx */ So the wrong value got saved and later restored back to the user. Fix it by pushing the correct value again (BP) for regs->cx. Fixes: 8c42819b61b8 ("x86/entry: Use PUSH_AND_CLEAR_REGS for compat") Reported-by: Guenter Roeck Signed-off-by: Josh Poimboeuf Signed-off-by: Peter Zijlstra (Intel) Tested-by: Guenter Roeck Link: https://lkml.kernel.org/r/b5a26592c9dd60bbacdf97974a7433fd802a5593.1652985970.git.jpoimboe@kernel.org --- arch/x86/entry/calling.h | 8 ++++---- arch/x86/entry/entry_64_compat.S | 2 +- 2 files changed, 5 insertions(+), 5 deletions(-) diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h index a97cc78..29b36e9 100644 --- a/arch/x86/entry/calling.h +++ b/arch/x86/entry/calling.h @@ -63,7 +63,7 @@ For 32-bit we have the following conventions - kernel is built with * for assembly code: */ -.macro PUSH_REGS rdx=%rdx rax=%rax save_ret=0 +.macro PUSH_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0 .if \save_ret pushq %rsi /* pt_regs->si */ movq 8(%rsp), %rsi /* temporarily store the return address in %rsi */ @@ -73,7 +73,7 @@ For 32-bit we have the following conventions - kernel is built with pushq %rsi /* pt_regs->si */ .endif pushq \rdx /* pt_regs->dx */ - pushq %rcx /* pt_regs->cx */ + pushq \rcx /* pt_regs->cx */ pushq \rax /* pt_regs->ax */ pushq %r8 /* pt_regs->r8 */ pushq %r9 /* pt_regs->r9 */ @@ -115,8 +115,8 @@ For 32-bit we have the following conventions - kernel is built with .endm -.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0 - PUSH_REGS rdx=\rdx, rax=\rax, save_ret=\save_ret +.macro PUSH_AND_CLEAR_REGS rdx=%rdx rcx=%rcx rax=%rax save_ret=0 + PUSH_REGS rdx=\rdx, rcx=\rcx, rax=\rax, save_ret=\save_ret CLEAR_REGS .endm diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index ed2be361..f76e674 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -200,7 +200,7 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL) SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL) movl %eax, %eax /* discard orig_ax high bits */ pushq %rax /* pt_regs->orig_ax */ - PUSH_AND_CLEAR_REGS rax=$-ENOSYS + PUSH_AND_CLEAR_REGS rcx=%rbp rax=$-ENOSYS UNWIND_HINT_REGS movq %rsp, %rdi -- 2.7.4