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x86/vsyscall: Reorganize the page fault emulation code

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With LASS, vsyscall page accesses will cause a #GP instead of a #PF.
Separate out the core vsyscall emulation code 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>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Link: https://patch.msgid.link/20260309181029.398498-2-sohil.mehta@intel.com
This commit is contained in:
Sohil Mehta
2026-03-09 11:10:25 -07:00
committed by Dave Hansen
parent 68400c1aaf
commit 3ddd2e12c7
3 changed files with 39 additions and 36 deletions
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66
arch/x86/entry/vsyscall/vsyscall_64.c
View File

@@ -111,43 +111,13 @@ 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.
@@ -280,6 +250,40 @@ 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) {
/* 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));
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

7
arch/x86/include/asm/vsyscall.h
View File

@@ -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;
}

2
arch/x86/mm/fault.c
View File

@@ -1314,7 +1314,7 @@ 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