CVE-2024-42240: x86/bhi: Avoid warning in #DB handler due to BHI mitigation
First published: Wed Aug 07 2024(Updated: )
In the Linux kernel, the following vulnerability has been resolved: x86/bhi: Avoid warning in #DB handler due to BHI mitigation When BHI mitigation is enabled, if SYSENTER is invoked with the TF flag set then entry_SYSENTER_compat() uses CLEAR_BRANCH_HISTORY and calls the clear_bhb_loop() before the TF flag is cleared. This causes the #DB handler (exc_debug_kernel()) to issue a warning because single-step is used outside the entry_SYSENTER_compat() function. To address this issue, entry_SYSENTER_compat() should use CLEAR_BRANCH_HISTORY after making sure the TF flag is cleared. The problem can be reproduced with the following sequence: $ cat sysenter_step.c int main() { asm("pushf; pop %ax; bts $8,%ax; push %ax; popf; sysenter"); } $ gcc -o sysenter_step sysenter_step.c $ ./sysenter_step Segmentation fault (core dumped) The program is expected to crash, and the #DB handler will issue a warning. Kernel log: WARNING: CPU: 27 PID: 7000 at arch/x86/kernel/traps.c:1009 exc_debug_kernel+0xd2/0x160 ... RIP: 0010:exc_debug_kernel+0xd2/0x160 ... Call Trace: <#DB> ? show_regs+0x68/0x80 ? __warn+0x8c/0x140 ? exc_debug_kernel+0xd2/0x160 ? report_bug+0x175/0x1a0 ? handle_bug+0x44/0x90 ? exc_invalid_op+0x1c/0x70 ? asm_exc_invalid_op+0x1f/0x30 ? exc_debug_kernel+0xd2/0x160 exc_debug+0x43/0x50 asm_exc_debug+0x1e/0x40 RIP: 0010:clear_bhb_loop+0x0/0xb0 ... </#DB> <TASK> ? entry_SYSENTER_compat_after_hwframe+0x6e/0x8d </TASK> [ bp: Massage commit message. ]
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Linux kernel | >=5.15.163<6.1.100 | |
| Linux Linux kernel | >=6.2<6.6.41 | |
| Linux Linux kernel | >=6.7<6.9.10 | |
| debian/linux | 5.10.223-1 5.10.226-1 6.1.115-1 6.1.112-1 6.11.9-1 6.11.10-1 |
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Reference Links
- https://git.kernel.org/stable/c/08518d48e5b744620524f0acd7c26c19bda7f513
- https://git.kernel.org/stable/c/a765679defe1dc1b8fa01928a6ad6361e72a1364
- https://git.kernel.org/stable/c/ac8b270b61d48fcc61f052097777e3b5e11591e0
- https://git.kernel.org/stable/c/dae3543db8f0cf8ac1a198c3bb4b6e3c24d576cf
- https://git.kernel.org/stable/c/db56615e96c439e13783d7715330e824b4fd4b84
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-42240
- https://nvd.nist.gov/vuln/detail/CVE-2024-42240
- https://launchpad.net/bugs/cve/CVE-2024-42240
- https://security-tracker.debian.org/tracker/CVE-2024-42240
- https://ubuntu.com/security/CVE-2024-42240
- https://git.kernel.org/linus/ac8b270b61d48fcc61f052097777e3b5e11591e0
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