[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v3 3/4] x86/spec: fix INDIRECT_THUNK option to only be set when build-enabled
Attempt to provide a more helpful error message when the user attempts to set spec-ctrl=bti-thunk option but the support is build-time disabled. While there also adjust the command line documentation to mention CONFIG_INDIRECT_THUNK instead of INDIRECT_THUNK. Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> --- Changes since v2: - Adjust documentation. - Use IS_ENABLED() instead of #ifdef. Changes since v1: - New in this version. --- docs/misc/xen-command-line.pandoc | 10 +++++----- xen/arch/x86/spec_ctrl.c | 7 ++++++- 2 files changed, 11 insertions(+), 6 deletions(-) diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc index be76be8d5365..02896598df6f 100644 --- a/docs/misc/xen-command-line.pandoc +++ b/docs/misc/xen-command-line.pandoc @@ -2417,11 +2417,11 @@ guests to use. performance reasons dom0 is unprotected by default. If it is necessary to protect dom0 too, boot with `spec-ctrl=ibpb-entry`. -If Xen was compiled with INDIRECT_THUNK support, `bti-thunk=` can be used to -select which of the thunks gets patched into the `__x86_indirect_thunk_%reg` -locations. The default thunk is `retpoline` (generally preferred), with the -alternatives being `jmp` (a `jmp *%reg` gadget, minimal overhead), and -`lfence` (an `lfence; jmp *%reg` gadget). +If Xen was compiled with `CONFIG_INDIRECT_THUNK` support, `bti-thunk=` can be +used to select which of the thunks gets patched into the +`__x86_indirect_thunk_%reg` locations. The default thunk is `retpoline` +(generally preferred), with the alternatives being `jmp` (a `jmp *%reg` gadget, +minimal overhead), and `lfence` (an `lfence; jmp *%reg` gadget). On hardware supporting IBRS (Indirect Branch Restricted Speculation), the `ibrs=` option can be used to force or prevent Xen using the feature itself. diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c index 5fae80774519..ca82b9e41ccd 100644 --- a/xen/arch/x86/spec_ctrl.c +++ b/xen/arch/x86/spec_ctrl.c @@ -241,7 +241,12 @@ static int __init cf_check parse_spec_ctrl(const char *s) { s += 10; - if ( !cmdline_strcmp(s, "retpoline") ) + if ( !IS_ENABLED(CONFIG_INDIRECT_THUNK) ) + { + no_config_param("INDIRECT_THUNK", "spec-ctrl=bti-thunk", s, ss); + rc = -EINVAL; + } + else if ( !cmdline_strcmp(s, "retpoline") ) opt_thunk = THUNK_RETPOLINE; else if ( !cmdline_strcmp(s, "lfence") ) opt_thunk = THUNK_LFENCE; -- 2.43.0
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