[PATCH] powerpc/pseries: Fix to clear security feature flags

[PATCH] powerpc/pseries: Fix to clear security feature flags

[Mauricio Faria de Oliveira]

The H_CPU_BEHAV_* flags should be checked for in the 'behaviour' field
of 'struct h_cpu_char_result' -- 'character' is for H_CPU_CHAR_* flags.

Found it by playing around with QEMU's implementation of the hypercall:

Example: 
  H_CPU_CHAR=0xf000000000000000
  H_CPU_BEHAV=0x0000000000000000

  This clears H_CPU_BEHAV_FAVOUR_SECURITY and H_CPU_BEHAV_L1D_FLUSH_PR
  so pseries_setup_rfi_flush() disables 'rfi_flush'; and it also clears
  H_CPU_CHAR_L1D_THREAD_PRIV flag.  So there is no RFI flush mitigation
  at all for cpu_show_meltdown() to report; but currently it does:

  Original kernel:

    # cat /sys/devices/system/cpu/vulnerabilities/meltdown
    Mitigation: RFI Flush

  Patched kernel:

    # cat /sys/devices/system/cpu/vulnerabilities/meltdown
    Not affected

Example:
  H_CPU_CHAR=0x0000000000000000
  H_CPU_BEHAV=0xf000000000000000

  This sets H_CPU_BEHAV_BNDS_CHK_SPEC_BAR so cpu_show_spectre_v1() should
  report vulnerable; but currently it doesn't:

  Original kernel:

    # cat /sys/devices/system/cpu/vulnerabilities/spectre_v1
    Not affected

  Patched kernel:

    # cat /sys/devices/system/cpu/vulnerabilities/spectre_v1
    Vulnerable

Fixes: f636c14790ea ("powerpc/pseries: Set or clear security feature flags")
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
---
 arch/powerpc/platforms/pseries/setup.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 1f12235..b11564f 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -484,13 +484,13 @@ static void init_cpu_char_feature_flags(struct h_cpu_char_result *result)
 	 * The features below are enabled by default, so we instead look to see
 	 * if firmware has *disabled* them, and clear them if so.
 	 */
-	if (!(result->character & H_CPU_BEHAV_FAVOUR_SECURITY))
+	if (!(result->behaviour & H_CPU_BEHAV_FAVOUR_SECURITY))
 		security_ftr_clear(SEC_FTR_FAVOUR_SECURITY);
 
-	if (!(result->character & H_CPU_BEHAV_L1D_FLUSH_PR))
+	if (!(result->behaviour & H_CPU_BEHAV_L1D_FLUSH_PR))
 		security_ftr_clear(SEC_FTR_L1D_FLUSH_PR);
 
-	if (!(result->character & H_CPU_BEHAV_BNDS_CHK_SPEC_BAR))
+	if (!(result->behaviour & H_CPU_BEHAV_BNDS_CHK_SPEC_BAR))
 		security_ftr_clear(SEC_FTR_BNDS_CHK_SPEC_BAR);
 }
 
-- 
1.8.3.1

Re: powerpc/pseries: Fix to clear security feature flags

[Michael Ellerman]

On Thu, 2018-03-29 at 18:32:11 UTC, Mauricio Faria de Oliveira wrote:
> The H_CPU_BEHAV_* flags should be checked for in the 'behaviour' field
> of 'struct h_cpu_char_result' -- 'character' is for H_CPU_CHAR_* flags.
> 
> Found it by playing around with QEMU's implementation of the hypercall:
> 
> Example: 
>   H_CPU_CHAR=0xf000000000000000
>   H_CPU_BEHAV=0x0000000000000000
> 
>   This clears H_CPU_BEHAV_FAVOUR_SECURITY and H_CPU_BEHAV_L1D_FLUSH_PR
>   so pseries_setup_rfi_flush() disables 'rfi_flush'; and it also clears
>   H_CPU_CHAR_L1D_THREAD_PRIV flag.  So there is no RFI flush mitigation
>   at all for cpu_show_meltdown() to report; but currently it does:
> 
>   Original kernel:
> 
>     # cat /sys/devices/system/cpu/vulnerabilities/meltdown
>     Mitigation: RFI Flush
> 
>   Patched kernel:
> 
>     # cat /sys/devices/system/cpu/vulnerabilities/meltdown
>     Not affected
> 
> Example:
>   H_CPU_CHAR=0x0000000000000000
>   H_CPU_BEHAV=0xf000000000000000
> 
>   This sets H_CPU_BEHAV_BNDS_CHK_SPEC_BAR so cpu_show_spectre_v1() should
>   report vulnerable; but currently it doesn't:
> 
>   Original kernel:
> 
>     # cat /sys/devices/system/cpu/vulnerabilities/spectre_v1
>     Not affected
> 
>   Patched kernel:
> 
>     # cat /sys/devices/system/cpu/vulnerabilities/spectre_v1
>     Vulnerable
> 
> Fixes: f636c14790ea ("powerpc/pseries: Set or clear security feature flags")
> Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/0f9bdfe3c77091e8704d2e510eb7c2

cheers