x86/insn: Extend error reporting from insn_fetch_from_user[_inatomic]()

The error reporting from the insn_fetch_from_user*() functions is not
very verbose. Extend it to include information on whether the linear
RIP could not be calculated or whether the memory access faulted.

This will be used in the SEV-ES code to propagate the correct
exception depending on what went wrong during instruction fetch.

 [ bp: Massage comments. ]

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210614135327.9921-6-joro@8bytes.org

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 4fd997bbf059af51d9211f3e250292612a5690d1..a1eeaa79bf2bfb5c4a770d0d6118eb985b40799f 100644 (file)
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -258,17 +258,17 @@ static int vc_fetch_insn_kernel(struct es_em_ctxt *ctxt,
 static enum es_result __vc_decode_user_insn(struct es_em_ctxt *ctxt)
 {
        char buffer[MAX_INSN_SIZE];
-       int res;
+       int insn_bytes;
 
-       res = insn_fetch_from_user_inatomic(ctxt->regs, buffer);
-       if (!res) {
+       insn_bytes = insn_fetch_from_user_inatomic(ctxt->regs, buffer);
+       if (insn_bytes <= 0) {
                ctxt->fi.vector     = X86_TRAP_PF;
                ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
                ctxt->fi.cr2        = ctxt->regs->ip;
                return ES_EXCEPTION;
        }
 
-       if (!insn_decode_from_regs(&ctxt->insn, ctxt->regs, buffer, res))
+       if (!insn_decode_from_regs(&ctxt->insn, ctxt->regs, buffer, insn_bytes))
                return ES_DECODE_FAILED;
 
        if (ctxt->insn.immediate.got)

diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 8daa70b0d2da276c54ed37eca88a292837d90cb1..576b47e7523db01290660a5b7c99f37dfb110a83 100644 (file)
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -346,14 +346,12 @@ bool fixup_umip_exception(struct pt_regs *regs)
        if (!regs)
                return false;
 
-       nr_copied = insn_fetch_from_user(regs, buf);
-
        /*
-        * The insn_fetch_from_user above could have failed if user code
-        * is protected by a memory protection key. Give up on emulation
-        * in such a case.  Should we issue a page fault?
+        * Give up on emulation if fetching the instruction failed. Should a
+        * page fault or a #GP be issued?
         */
-       if (!nr_copied)
+       nr_copied = insn_fetch_from_user(regs, buf);
+       if (nr_copied <= 0)
                return false;
 
        if (!insn_decode_from_regs(&insn, regs, buf, nr_copied))

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 4eecb9c7c6a056206984d2b62c0e323471014a4a..a1d24fdc07cf0280ab33cabe0e573f4795049820 100644 (file)
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -1448,9 +1448,9 @@ static int insn_get_effective_ip(struct pt_regs *regs, unsigned long *ip)
  *
  * Returns:
  *
- * Number of instruction bytes copied.
- *
- * 0 if nothing was copied.
+ * - number of instruction bytes copied.
+ * - 0 if nothing was copied.
+ * - -EINVAL if the linear address of the instruction could not be calculated
  */
 int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
 {
@@ -1458,7 +1458,7 @@ int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
        int not_copied;
 
        if (insn_get_effective_ip(regs, &ip))
-               return 0;
+               return -EINVAL;
 
        not_copied = copy_from_user(buf, (void __user *)ip, MAX_INSN_SIZE);
 
@@ -1476,9 +1476,9 @@ int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
  *
  * Returns:
  *
- * Number of instruction bytes copied.
- *
- * 0 if nothing was copied.
+ *  - number of instruction bytes copied.
+ *  - 0 if nothing was copied.
+ *  - -EINVAL if the linear address of the instruction could not be calculated.
  */
 int insn_fetch_from_user_inatomic(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
 {
@@ -1486,7 +1486,7 @@ int insn_fetch_from_user_inatomic(struct pt_regs *regs, unsigned char buf[MAX_IN
        int not_copied;
 
        if (insn_get_effective_ip(regs, &ip))
-               return 0;
+               return -EINVAL;
 
        not_copied = __copy_from_user_inatomic(buf, (void __user *)ip, MAX_INSN_SIZE);