diff options
| author | Pawan Gupta <pawan.kumar.gupta@linux.intel.com> | 2024-09-26 09:10:31 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2024-10-09 09:42:30 +0200 |
| commit | e4d2102018542e3ae5e297bc6e229303abff8a0f (patch) | |
| tree | 5452bb479a33f571b9a3cf45fa25baa2151ee4b2 /arch | |
| parent | 48a2440d0f20c826b884e04377ccc1e4696c84e9 (diff) | |
| download | linux-stable-e4d2102018542e3ae5e297bc6e229303abff8a0f.tar.gz linux-stable-e4d2102018542e3ae5e297bc6e229303abff8a0f.tar.bz2 linux-stable-e4d2102018542e3ae5e297bc6e229303abff8a0f.zip | |
x86/bugs: Use code segment selector for VERW operand
Robert Gill reported below #GP in 32-bit mode when dosemu software was
executing vm86() system call:
general protection fault: 0000 [#1] PREEMPT SMP
CPU: 4 PID: 4610 Comm: dosemu.bin Not tainted 6.6.21-gentoo-x86 #1
Hardware name: Dell Inc. PowerEdge 1950/0H723K, BIOS 2.7.0 10/30/2010
EIP: restore_all_switch_stack+0xbe/0xcf
EAX: 00000000 EBX: 00000000 ECX: 00000000 EDX: 00000000
ESI: 00000000 EDI: 00000000 EBP: 00000000 ESP: ff8affdc
DS: 0000 ES: 0000 FS: 0000 GS: 0033 SS: 0068 EFLAGS: 00010046
CR0: 80050033 CR2: 00c2101c CR3: 04b6d000 CR4: 000406d0
Call Trace:
show_regs+0x70/0x78
die_addr+0x29/0x70
exc_general_protection+0x13c/0x348
exc_bounds+0x98/0x98
handle_exception+0x14d/0x14d
exc_bounds+0x98/0x98
restore_all_switch_stack+0xbe/0xcf
exc_bounds+0x98/0x98
restore_all_switch_stack+0xbe/0xcf
This only happens in 32-bit mode when VERW based mitigations like MDS/RFDS
are enabled. This is because segment registers with an arbitrary user value
can result in #GP when executing VERW. Intel SDM vol. 2C documents the
following behavior for VERW instruction:
#GP(0) - If a memory operand effective address is outside the CS, DS, ES,
FS, or GS segment limit.
CLEAR_CPU_BUFFERS macro executes VERW instruction before returning to user
space. Use %cs selector to reference VERW operand. This ensures VERW will
not #GP for an arbitrary user %ds.
[ mingo: Fixed the SOB chain. ]
Fixes: a0e2dab44d22 ("x86/entry_32: Add VERW just before userspace transition")
Reported-by: Robert Gill <rtgill82@gmail.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com
Cc: stable@vger.kernel.org # 5.10+
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218707
Closes: https://lore.kernel.org/all/8c77ccfd-d561-45a1-8ed5-6b75212c7a58@leemhuis.info/
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Suggested-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/include/asm/nospec-branch.h | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index ff5f1ecc7d1e..96b410b1d4e8 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -323,7 +323,16 @@ * Note: Only the memory operand variant of VERW clears the CPU buffers. */ .macro CLEAR_CPU_BUFFERS - ALTERNATIVE "", __stringify(verw _ASM_RIP(mds_verw_sel)), X86_FEATURE_CLEAR_CPU_BUF +#ifdef CONFIG_X86_64 + ALTERNATIVE "", "verw mds_verw_sel(%rip)", X86_FEATURE_CLEAR_CPU_BUF +#else + /* + * In 32bit mode, the memory operand must be a %cs reference. The data + * segments may not be usable (vm86 mode), and the stack segment may not + * be flat (ESPFIX32). + */ + ALTERNATIVE "", "verw %cs:mds_verw_sel", X86_FEATURE_CLEAR_CPU_BUF +#endif .endm #ifdef CONFIG_X86_64 |