Messages in this thread Patch in this message | | | From | "Xin Li (Intel)" <> | Subject | [PATCH v1 1/1] x86/entry/64: Skip SYSRET validation tests when FRED is enabled | Date | Tue, 2 Apr 2024 23:24:03 -0700 |
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Don't do SYSRET validation tests when FRED is enabled, since ERETU is the only legit instruction to return to user level.
Signed-off-by: Xin Li (Intel) <xin@zytor.com> --- arch/x86/entry/common.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 6356060caaf3..1c3944eb9901 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -72,7 +72,7 @@ static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr) return false; } -/* Returns true to return using SYSRET, or false to use IRET */ +/* Returns true to return using SYSRET, or false to use IRET/ERETU */ __visible noinstr bool do_syscall_64(struct pt_regs *regs, int nr) { add_random_kstack_offset(); @@ -88,6 +88,10 @@ __visible noinstr bool do_syscall_64(struct pt_regs *regs, int nr) instrumentation_end(); syscall_exit_to_user_mode(regs); + /* No test for FRED, which returns to user level with ERETU only */ + if (cpu_feature_enabled(X86_FEATURE_FRED)) + return false; + /* * Check that the register state is valid for using SYSRET to exit * to userspace. Otherwise use the slower but fully capable IRET @@ -325,7 +329,7 @@ static noinstr bool __do_fast_syscall_32(struct pt_regs *regs) return true; } -/* Returns true to return using SYSEXIT/SYSRETL, or false to use IRET */ +/* Returns true to return using SYSEXIT/SYSRETL, or false to use IRET/ERETU */ __visible noinstr bool do_fast_syscall_32(struct pt_regs *regs) { /* @@ -346,6 +350,10 @@ __visible noinstr bool do_fast_syscall_32(struct pt_regs *regs) if (!__do_fast_syscall_32(regs)) return false; + /* No test for FRED, which returns to user level with ERETU only */ + if (cpu_feature_enabled(X86_FEATURE_FRED)) + return false; + /* * Check that the register state is valid for using SYSRETL/SYSEXIT * to exit to userspace. Otherwise use the slower but fully capable base-commit: 65d1240b6728b38e4d2068d6738a17e4ee4351f5 -- 2.44.0
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