5.4-stable review patch. If anyone has any objections, please let me know.
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From: Kirill A. Shutemov kirill.shutemov@linux.intel.com
[ Upstream commit 8ba38a7a9a699905b84fa97578a8291010dec273 ]
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... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/entry/vsyscall/vsyscall_64.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c index 86e5a1c1055ff..85e80f0a8b15e 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; @@ -136,13 +141,19 @@ bool emulate_vsyscall(unsigned long error_code, return false; }
+ /* + * 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");