The following commit has been merged into the x86/entry branch of tip: Commit-ID: 1a09a27153f91cd7676b2d4ca574577572a8c999 Gitweb: https://git.kernel.org/tip/1a09a27153f91cd7676b2d4ca574577572a8c999 Author: Brian Gerst <brgerst@xxxxxxxxx> AuthorDate: Wed, 11 Oct 2023 18:43:51 -04:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Fri, 13 Oct 2023 13:05:28 +02:00 x86/entry/32: Clean up syscall fast exit tests Merge compat and native code and clarify comments. No change in functionality expected. Signed-off-by: Brian Gerst <brgerst@xxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Uros Bizjak <ubizjak@xxxxxxxxx> Link: https://lore.kernel.org/r/20231011224351.130935-4-brgerst@xxxxxxxxx --- arch/x86/entry/common.c | 48 ++++++++++++++++++---------------------- 1 file changed, 22 insertions(+), 26 deletions(-) diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 4c7154d..d813160 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -255,34 +255,30 @@ __visible noinstr bool do_fast_syscall_32(struct pt_regs *regs) if (!__do_fast_syscall_32(regs)) return false; -#ifdef CONFIG_X86_64 /* - * Opportunistic SYSRETL: if possible, try to return using SYSRETL. - * SYSRETL is available on all 64-bit CPUs, so we don't need to - * bother with SYSEXIT. - * - * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, - * because the ECX fixup above will ensure that this is essentially - * never the case. + * Check that the register state is valid for using SYSRETL/SYSEXIT + * to exit to userspace. Otherwise use the slower but fully capable + * IRET exit path. */ - return regs->cs == __USER32_CS && regs->ss == __USER_DS && - regs->ip == landing_pad && - (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0; -#else - /* - * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT. - * - * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, - * because the ECX fixup above will ensure that this is essentially - * never the case. - * - * We don't allow syscalls at all from VM86 mode, but we still - * need to check VM, because we might be returning from sys_vm86. - */ - return regs->cs == __USER_CS && regs->ss == __USER_DS && - regs->ip == landing_pad && - (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0; -#endif + + /* XEN PV guests always use the IRET path */ + if (cpu_feature_enabled(X86_FEATURE_XENPV)) + return false; + + /* EIP must point to the VDSO landing pad */ + if (unlikely(regs->ip != landing_pad)) + return false; + + /* CS and SS must match the values set in MSR_STAR */ + if (unlikely(regs->cs != __USER32_CS || regs->ss != __USER_DS)) + return false; + + /* If the TF, RF, or VM flags are set, use IRET */ + if (unlikely(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM))) + return false; + + /* Use SYSRETL/SYSEXIT to exit to userspace */ + return true; } /* Returns true to return using SYSEXIT/SYSRETL, or false to use IRET */
|