Commit 3ddd2e12 authored by Sohil Mehta's avatar Sohil Mehta Committed by Dave Hansen
Browse files

x86/vsyscall: Reorganize the page fault emulation code 



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: default avatarSohil Mehta <sohil.mehta@intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarH. Peter Anvin (Intel) <hpa@zytor.com>
Acked-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Tested-by: default avatarMaciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Link: https://patch.msgid.link/20260309181029.398498-2-sohil.mehta@intel.com
parent 68400c1a

arch/x86/entry/vsyscall/vsyscall_64.c

+35 −31
Original line number Diff line number Diff line
@@ -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

arch/x86/include/asm/vsyscall.h

+3 −4
Original line number Diff line number Diff line
@@ -14,11 +14,10 @@ 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,

static inline bool emulate_vsyscall_pf(unsigned long error_code,

				       struct pt_regs *regs, unsigned long address)

{

	return false;

arch/x86/mm/fault.c

+1 −1
Original line number Diff line number Diff line
@@ -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