Commit-ID: 918ce325098a4eef99daad7b6796da33cebaf03a
Gitweb: https://git.kernel.org/tip/918ce325098a4eef99daad7b6796da33cebaf03a
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Wed, 26 Jun 2019 21:45:04 -0700
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 28 Jun 2019 00:04:39 +0200
x86/vsyscall: Show something useful on a read fault
Just segfaulting the application when it tries to read the vsyscall page in
xonly mode is not helpful for those who need to debug it.
Emit a hint.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Florian Weimer <fweimer@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/8016afffe0eab497be32017ad7f6f7030dc3ba66.1561610354.git.luto@xxxxxxxxxx
---
arch/x86/entry/vsyscall/vsyscall_64.c | 19 ++++++++++++++++++-
arch/x86/include/asm/vsyscall.h | 6 ++++--
arch/x86/mm/fault.c | 11 +++++------
3 files changed, 27 insertions(+), 9 deletions(-)
diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index fedd7628f3a6..9c58ab807aeb 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -117,7 +117,8 @@ static bool write_ok_or_segv(unsigned long ptr, size_t size)
}
}
-bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
+bool emulate_vsyscall(unsigned long error_code,
+ struct pt_regs *regs, unsigned long address)
{
struct task_struct *tsk;
unsigned long caller;
@@ -126,6 +127,22 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
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;
+
+ if (!(error_code & X86_PF_INSTR)) {
+ /* 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;
+ }
+
/*
* 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.
diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index b986b2ca688a..ab60a71a8dcb 100644
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -13,10 +13,12 @@ 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(struct pt_regs *regs, unsigned long address);
+extern bool emulate_vsyscall(unsigned long error_code,
+ struct pt_regs *regs, unsigned long address);
#else
static inline void map_vsyscall(void) {}
-static inline bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
+static inline bool emulate_vsyscall(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 46df4c6aae46..288a5462076f 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1369,16 +1369,15 @@ void do_user_addr_fault(struct pt_regs *regs,
#ifdef CONFIG_X86_64
/*
- * Instruction fetch faults in the vsyscall page might need
- * emulation. The vsyscall page is at a high address
- * (>PAGE_OFFSET), but is considered to be part of the user
- * address space.
+ * Faults in the vsyscall page might need emulation. The
+ * vsyscall page is at a high address (>PAGE_OFFSET), but is
+ * considered to be part of the user address space.
*
* The vsyscall page does not have a "real" VMA, so do this
* emulation before we go searching for VMAs.
*/
- if ((hw_error_code & X86_PF_INSTR) && is_vsyscall_vaddr(address)) {
- if (emulate_vsyscall(regs, address))
+ if (is_vsyscall_vaddr(address)) {
+ if (emulate_vsyscall(hw_error_code, regs, address))
return;
}
#endif
|