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Subject[PATCH v9 25/29] x86/umip: Force a page fault when unable to copy emulated result to user
Date
fixup_umip_exception() will be called from do_general_protection(). If the
former returns false, the latter will issue a SIGSEGV with SEND_SIG_PRIV.
However, when emulation is successful but the emulated result cannot be
copied to user space memory, it is more accurate to issue a SIGSEGV with
SEGV_MAPERR with the offending address. A new function, inspired in
force_sig_info_fault(), is introduced to model the page fault.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chen Yucong <slaoub@gmail.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: x86@kernel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
---
arch/x86/kernel/umip.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 43 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 1f338cb..6d07eb5 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -187,6 +187,41 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
}

/**
+ * force_sig_info_umip_fault() - Force a SIGSEGV with SEGV_MAPERR
+ * @addr: Address that caused the signal
+ * @regs: Register set containing the instruction pointer
+ *
+ * Force a SIGSEGV signal with SEGV_MAPERR as the error code. This function is
+ * intended to be used to provide a segmentation fault when the result of the
+ * UMIP emulation could not be copied to the user space memory.
+ *
+ * Returns: none
+ */
+static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs)
+{
+ siginfo_t info;
+ struct task_struct *tsk = current;
+
+ tsk->thread.cr2 = (unsigned long)addr;
+ tsk->thread.error_code = X86_PF_USER | X86_PF_WRITE;
+ tsk->thread.trap_nr = X86_TRAP_PF;
+
+ info.si_signo = SIGSEGV;
+ info.si_errno = 0;
+ info.si_code = SEGV_MAPERR;
+ info.si_addr = addr;
+ force_sig_info(SIGSEGV, &info, tsk);
+
+ if (!(show_unhandled_signals && unhandled_signal(tsk, SIGSEGV)))
+ return;
+
+ pr_err_ratelimited("%s[%d] umip emulation segfault ip:%lx sp:%lx error:%x in %lx\n",
+ tsk->comm, task_pid_nr(tsk), regs->ip,
+ regs->sp, X86_PF_USER | X86_PF_WRITE,
+ regs->ip);
+}
+
+/**
* fixup_umip_exception() - Fixup #GP faults caused by UMIP
* @regs: Registers as saved when entering the #GP trap
*
@@ -299,8 +334,14 @@ bool fixup_umip_exception(struct pt_regs *regs)
return false;

nr_copied = copy_to_user(uaddr, dummy_data, dummy_data_size);
- if (nr_copied > 0)
- return false;
+ if (nr_copied > 0) {
+ /*
+ * If copy fails, send a signal and tell caller that
+ * fault was fixed up.
+ */
+ force_sig_info_umip_fault(uaddr, regs);
+ return true;
+ }
}

/* increase IP to let the program keep going */
--
2.7.4
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