[Xen-changelog] [xen stable-4.8] x86/cmdline: Introduce a command line option to disable IBRS/IBPB, STIBP and IBPB

[patchbot@xxxxxxx]

commit 532ccf4fd55cfd916f56279a71852585d726ab23
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Feb 8 12:50:16 2018 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 8 12:50:16 2018 +0100

    x86/cmdline: Introduce a command line option to disable IBRS/IBPB, STIBP 
and IBPB
    
    Instead of gaining yet another top level boolean, introduce a more generic
    cpuid= option.  Also introduce a helper function to parse a generic boolean
    value.
    
    This is part of XSA-254.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    
    xen/cmdline: Fix parse_boolean() for unadorned values
    
    A command line such as "cpuid=no-ibrsb,no-stibp" tickles a bug in
    parse_boolean() because the separating comma fails the NUL case.
    
    Instead, check for slen == nlen which accounts for the boundary (if any)
    passed via the 'e' parameter.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 7850b1c00749df834ea2ad0c1f5d9364c4838795
    master date: 2018-01-16 17:45:50 +0000
    master commit: ac37ec1ddef234eeba6f438c29ff687c64962ebd
    master date: 2018-01-31 10:47:12 +0000
---
 docs/misc/xen-command-line.markdown | 12 ++++++++++++
 xen/arch/x86/cpuid.c                | 35 +++++++++++++++++++++++++++++++++++
 xen/common/kernel.c                 | 36 ++++++++++++++++++++++++++++++++++++
 xen/include/xen/lib.h               |  7 +++++++
 4 files changed, 90 insertions(+)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index 5ecb5eb..709e4de 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -434,6 +434,18 @@ choice of `dom0-kernel` is deprecated and not supported by 
all Dom0 kernels.
   respectively.
 * `verbose` option can be included as a string or also as `verbose=<integer>`
 
+### cpuid (x86)
+> `= List of comma separated booleans`
+
+This option allows for fine tuning of the facilities Xen will use, after
+accounting for hardware capabilities as enumerated via CPUID.
+
+Currently accepted:
+
+The Speculation Control hardware features `ibrsb`, `stibp`, `ibpb` are used by
+default if avaiable.  They can be ignored, e.g. `no-ibrsb`, at which point Xen
+won't use them itself, and won't offer them to guests.
+
 ### cpuid\_mask\_cpu (AMD only)
 > `= fam_0f_rev_c | fam_0f_rev_d | fam_0f_rev_e | fam_0f_rev_f | fam_0f_rev_g 
 > | fam_10_rev_b | fam_10_rev_c | fam_11_rev_b`
 
diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index 63b2db9..7a7c8de 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -17,6 +17,41 @@ uint32_t __read_mostly raw_featureset[FSCAPINTS];
 uint32_t __read_mostly pv_featureset[FSCAPINTS];
 uint32_t __read_mostly hvm_featureset[FSCAPINTS];
 
+static int __init parse_xen_cpuid(const char *s)
+{
+    const char *ss;
+    int val, rc = 0;
+
+    do {
+        ss = strchr(s, ',');
+        if ( !ss )
+            ss = strchr(s, '\0');
+
+        if ( (val = parse_boolean("ibpb", s, ss)) >= 0 )
+        {
+            if ( !val )
+                setup_clear_cpu_cap(X86_FEATURE_IBPB);
+        }
+        else if ( (val = parse_boolean("ibrsb", s, ss)) >= 0 )
+        {
+            if ( !val )
+                setup_clear_cpu_cap(X86_FEATURE_IBRSB);
+        }
+        else if ( (val = parse_boolean("stibp", s, ss)) >= 0 )
+        {
+            if ( !val )
+                setup_clear_cpu_cap(X86_FEATURE_STIBP);
+        }
+        else
+            rc = -EINVAL;
+
+        s = ss + 1;
+    } while ( *ss );
+
+    return rc;
+}
+custom_param("cpuid", parse_xen_cpuid);
+
 static void __init sanitise_featureset(uint32_t *fs)
 {
     /* for_each_set_bit() uses unsigned longs.  Extend with zeroes. */
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index d0edb13..ed49c62 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -166,6 +166,42 @@ int __init parse_bool(const char *s)
     return -1;
 }
 
+int parse_boolean(const char *name, const char *s, const char *e)
+{
+    size_t slen, nlen;
+    int val = !!strncmp(s, "no-", 3);
+
+    if ( !val )
+        s += 3;
+
+    slen = e ? ({ ASSERT(e >= s); e - s; }) : strlen(s);
+    nlen = strlen(name);
+
+    /* Does s now start with name? */
+    if ( slen < nlen || strncmp(s, name, nlen) )
+        return -1;
+
+    /* Exact, unadorned name?  Result depends on the 'no-' prefix. */
+    if ( slen == nlen )
+        return val;
+
+    /* =$SOMETHING?  Defer to the regular boolean parsing. */
+    if ( s[nlen] == '=' )
+    {
+        char buf[8];
+
+        s += nlen + 1;
+        if ( e <= s || e - s >= ARRAY_SIZE(buf) )
+            return -1;
+        memcpy(buf, s, e - s);
+        buf[e - s] = 0;
+        return parse_bool(buf);
+    }
+
+    /* Unrecognised.  Give up. */
+    return -1;
+}
+
 unsigned int tainted;
 
 /**
diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index d1171b7..b9d1c87 100644
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -68,6 +68,13 @@ struct domain;
 void cmdline_parse(const char *cmdline);
 int parse_bool(const char *s);
 
+/**
+ * Given a specific name, parses a string of the form:
+ *   [no-]$NAME[=...]
+ * returning 0 or 1 for a recognised boolean, or -1 for an error.
+ */
+int parse_boolean(const char *name, const char *s, const char *e);
+
 /*#define DEBUG_TRACE_DUMP*/
 #ifdef DEBUG_TRACE_DUMP
 extern void debugtrace_dump(void);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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