kernel.git/arch/x86/entry/common.c, branch linux-6.10.y

x86/fred: Fix INT80 emulation for FRED

2024-04-18T08:37:11Z

Add a FRED-specific INT80 handler and document why it differs from the current one. Eventually, the common bits will be unified once FRED hw is available and it turns out that no further changes are needed but for now, keep the handlers separate for everyone's sanity's sake. [ bp: Zap duplicated commit message, massage. ] Fixes: 55617fb991df ("x86/entry: Do not allow external 0x80 interrupts") Suggested-by: H. Peter Anvin (Intel) Signed-off-by: Xin Li (Intel) Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20240417174731.4189592-1-xin@zytor.com

x86/bhi: Add support for clearing branch history at syscall entry

2024-04-08T17:27:05Z

Branch History Injection (BHI) attacks may allow a malicious application to influence indirect branch prediction in kernel by poisoning the branch history. eIBRS isolates indirect branch targets in ring0. The BHB can still influence the choice of indirect branch predictor entry, and although branch predictor entries are isolated between modes when eIBRS is enabled, the BHB itself is not isolated between modes. Alder Lake and new processors supports a hardware control BHI_DIS_S to mitigate BHI. For older processors Intel has released a software sequence to clear the branch history on parts that don't support BHI_DIS_S. Add support to execute the software sequence at syscall entry and VMexit to overwrite the branch history. For now, branch history is not cleared at interrupt entry, as malicious applications are not believed to have sufficient control over the registers, since previous register state is cleared at interrupt entry. Researchers continue to poke at this area and it may become necessary to clear at interrupt entry as well in the future. This mitigation is only defined here. It is enabled later. Signed-off-by: Pawan Gupta Co-developed-by: Daniel Sneddon Signed-off-by: Daniel Sneddon Signed-off-by: Thomas Gleixner Reviewed-by: Alexandre Chartre Reviewed-by: Josh Poimboeuf

x86/syscall: Don't force use of indirect calls for system calls

2024-04-08T17:27:05Z

Make build a switch statement instead, and the compiler can either decide to generate an indirect jump, or - more likely these days due to mitigations - just a series of conditional branches. Yes, the conditional branches also have branch prediction, but the branch prediction is much more controlled, in that it just causes speculatively running the wrong system call (harmless), rather than speculatively running possibly wrong random less controlled code gadgets. This doesn't mitigate other indirect calls, but the system call indirection is the first and most easily triggered case. Signed-off-by: Linus Torvalds Signed-off-by: Daniel Sneddon Signed-off-by: Thomas Gleixner Reviewed-by: Josh Poimboeuf

x86/entry: Do not allow external 0x80 interrupts

2023-12-07T17:51:29Z

The INT 0x80 instruction is used for 32-bit x86 Linux syscalls. The kernel expects to receive a software interrupt as a result of the INT 0x80 instruction. However, an external interrupt on the same vector also triggers the same codepath. An external interrupt on vector 0x80 will currently be interpreted as a 32-bit system call, and assuming that it was a user context. Panic on external interrupts on the vector. To distinguish software interrupts from external ones, the kernel checks the APIC ISR bit relevant to the 0x80 vector. For software interrupts, this bit will be 0. Signed-off-by: Thomas Gleixner Signed-off-by: Kirill A. Shutemov Signed-off-by: Dave Hansen Reviewed-by: Borislav Petkov (AMD) Cc: # v6.0+

x86/entry: Convert INT 0x80 emulation to IDTENTRY

2023-12-07T17:51:29Z

There is no real reason to have a separate ASM entry point implementation for the legacy INT 0x80 syscall emulation on 64-bit. IDTENTRY provides all the functionality needed with the only difference that it does not: - save the syscall number (AX) into pt_regs::orig_ax - set pt_regs::ax to -ENOSYS Both can be done safely in the C code of an IDTENTRY before invoking any of the syscall related functions which depend on this convention. Aside of ASM code reduction this prepares for detecting and handling a local APIC injected vector 0x80. [ kirill.shutemov: More verbose comments ] Suggested-by: Linus Torvalds Signed-off-by: Thomas Gleixner Signed-off-by: Kirill A. Shutemov Signed-off-by: Dave Hansen Reviewed-by: Borislav Petkov (AMD) Cc: # v6.0+

x86/entry/32: Clean up syscall fast exit tests

2023-10-13T11:05:28Z

Merge compat and native code and clarify comments. No change in functionality expected. Signed-off-by: Brian Gerst Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Josh Poimboeuf Cc: Uros Bizjak Link: https://lore.kernel.org/r/20231011224351.130935-4-brgerst@gmail.com

x86/entry/64: Use TASK_SIZE_MAX for canonical RIP test

2023-10-13T11:05:28Z

Using shifts to determine if an address is canonical is difficult for the compiler to optimize when the virtual address width is variable (LA57 feature) without using inline assembly. Instead, compare RIP against TASK_SIZE_MAX. The only user executable address outside of that range is the deprecated vsyscall page, which can fall back to using IRET. Signed-off-by: Brian Gerst Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Josh Poimboeuf Cc: Uros Bizjak Link: https://lore.kernel.org/r/20231011224351.130935-3-brgerst@gmail.com

x86/entry/64: Convert SYSRET validation tests to C

2023-10-13T11:05:28Z

No change in functionality expected. Signed-off-by: Brian Gerst Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Josh Poimboeuf Cc: Uros Bizjak Link: https://lore.kernel.org/r/20231011224351.130935-2-brgerst@gmail.com

x86/entry/32: Remove SEP test for SYSEXIT

2023-10-05T08:06:43Z

SEP must be already be present in order for do_fast_syscall_32() to be called on native 32-bit, so checking it again is unnecessary. Signed-off-by: Brian Gerst Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230721161018.50214-6-brgerst@gmail.com

x86/entry/32: Convert do_fast_syscall_32() to bool return type

2023-10-05T08:06:42Z

Doesn't have to be 'long' - this simplifies the code a bit. Signed-off-by: Brian Gerst Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230721161018.50214-5-brgerst@gmail.com