diff options
| author | Kirill A. Shutemov <kirill.shutemov@linux.intel.com> | 2025-06-24 17:59:18 +0300 |
|---|---|---|
| committer | Dave Hansen <dave.hansen@linux.intel.com> | 2025-08-13 15:02:12 -0700 |
| commit | 8ba38a7a9a699905b84fa97578a8291010dec273 (patch) | |
| tree | b7ef847c1d1b5ce238c423c08590c8ebe0288f1c | |
| parent | 8f5ae30d69d7543eee0d70083daf4de8fe15d585 (diff) | |
x86/vsyscall: Do not require X86_PF_INSTR to emulate vsyscall
emulate_vsyscall() expects to see X86_PF_INSTR in PFEC on a vsyscall
page fault, but the CPU does not report X86_PF_INSTR if neither
X86_FEATURE_NX nor X86_FEATURE_SMEP are enabled.
X86_FEATURE_NX should be enabled on nearly all 64-bit CPUs, except for
early P4 processors that did not support this feature.
Instead of explicitly checking for X86_PF_INSTR, compare the fault
address to RIP.
On machines with X86_FEATURE_NX enabled, issue a warning if RIP is equal
to fault address but X86_PF_INSTR is absent.
[ dhansen: flesh out code comments ]
Originally-by: Dave Hansen <dave.hansen@intel.com>
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Link: https://lore.kernel.org/all/bd81a98b-f8d4-4304-ac55-d4151a1a77ab@intel.com
Link: https://lore.kernel.org/all/20250624145918.2720487-1-kirill.shutemov%40linux.intel.com
| -rw-r--r-- | arch/x86/entry/vsyscall/vsyscall_64.c | 17 |
1 files changed, 14 insertions, 3 deletions
diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c index c9103a6fa06e..6e6c0a740837 100644 --- a/arch/x86/entry/vsyscall/vsyscall_64.c +++ b/arch/x86/entry/vsyscall/vsyscall_64.c @@ -124,7 +124,12 @@ bool emulate_vsyscall(unsigned long error_code, if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER) return false; - if (!(error_code & X86_PF_INSTR)) { + /* + * Assume that faults at regs->ip are because of an + * instruction fetch. Return early and avoid + * emulation for faults during data accesses: + */ + if (address != regs->ip) { /* Failed vsyscall read */ if (vsyscall_mode == EMULATE) return false; @@ -137,12 +142,18 @@ bool emulate_vsyscall(unsigned long error_code, } /* + * X86_PF_INSTR is only set when NX is supported. When + * available, use it to double-check that the emulation code + * is only being used for instruction fetches: + */ + if (cpu_feature_enabled(X86_FEATURE_NX)) + WARN_ON_ONCE(!(error_code & X86_PF_INSTR)); + + /* * No point in checking CS -- the only way to get here is a user mode * trap to a high address, which means that we're in 64-bit user code. */ - WARN_ON_ONCE(address != regs->ip); - if (vsyscall_mode == NONE) { warn_bad_vsyscall(KERN_INFO, regs, "vsyscall attempted with vsyscall=none"); |