[PATCH v10 08/15] x86/vsyscall: Reorganize the page fault emulation code

Sohil Mehta
2025-10-07T06:54:03Z

Separate out the actual vsyscall emulation from the #PF specific
handling in preparation for the upcoming #GP emulation.

No functional change intended.

Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
---
v10:
- Modify the code flow slightly to make it easier to follow.
---
arch/x86/entry/vsyscall/vsyscall_64.c | 63 ++++++++++++++-------------
arch/x86/include/asm/vsyscall.h | 7 ++-
arch/x86/mm/fault.c | 2 +-
3 files changed, 36 insertions(+), 36 deletions(-)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index 6e6c0a740837..4c3f49bf39e6 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -112,43 +112,13 @@ static bool write_ok_or_segv(unsigned long ptr, size_t size)
}
}

-bool emulate_vsyscall(unsigned long error_code,
- struct pt_regs *regs, unsigned long address)
+static bool __emulate_vsyscall(struct pt_regs *regs, unsigned long address)
{
unsigned long caller;
int vsyscall_nr, syscall_nr, tmp;
long ret;
unsigned long orig_dx;

- /* Write faults or kernel-privilege faults never get fixed up. */
- if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
- return false;
-
- /*
- * 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;
-
- /*
- * User code tried and failed to read the vsyscall page.
- */
- warn_bad_vsyscall(KERN_INFO, regs, "vsyscall read attempt denied -- look up the vsyscall kernel parameter if you need a workaround");
- 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.
@@ -281,6 +251,37 @@ bool emulate_vsyscall(unsigned long error_code,
return true;
}

+bool emulate_vsyscall_pf(unsigned long error_code, struct pt_regs *regs,
+ unsigned long address)
+{
+ /* Write faults or kernel-privilege faults never get fixed up. */
+ if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
+ return false;
+
+ /*
+ * 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) {
+ /* User code tried and failed to read the vsyscall page. */
+ if (vsyscall_mode != EMULATE)
+ warn_bad_vsyscall(KERN_INFO, regs, "vsyscall read attempt denied -- look up the vsyscall kernel parameter if you need a workaround");
+
+ 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));
+
+ return __emulate_vsyscall(regs, address);
+}
+
/*
* A pseudo VMA to allow ptrace access for the vsyscall page. This only
* covers the 64bit vsyscall page now. 32bit has a real VMA now and does
diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index 472f0263dbc6..f34902364972 100644
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -14,12 +14,11 @@ extern void set_vsyscall_pgtable_user_bits(pgd_t *root);
* Called on instruction fetch fault in vsyscall page.
* Returns true if handled.
*/
-extern bool emulate_vsyscall(unsigned long error_code,
- struct pt_regs *regs, unsigned long address);
+bool emulate_vsyscall_pf(unsigned long error_code, struct pt_regs *regs, unsigned long address);
#else
static inline void map_vsyscall(void) {}
-static inline bool emulate_vsyscall(unsigned long error_code,
- struct pt_regs *regs, unsigned long address)
+static inline bool emulate_vsyscall_pf(unsigned long error_code,
+ struct pt_regs *regs, unsigned long address)
{
return false;
}
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 998bd807fc7b..fbcc2da75fd6 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1316,7 +1316,7 @@ void do_user_addr_fault(struct pt_regs *regs,
* to consider the PF_PK bit.
*/
if (is_vsyscall_vaddr(address)) {
- if (emulate_vsyscall(error_code, regs, address))
+ if (emulate_vsyscall_pf(error_code, regs, address))
return;
}
#endif
--
2.43.0