[PATCH 4.9 42/61] powerpc/pseries: Fix clearing of security feature flags

Greg Kroah-Hartman
2018-06-05T17:06:12Z

From: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>

commit 0f9bdfe3c77091e8704d2e510eb7c2c2c6cde524 upstream.

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

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

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

Brown-paper-bag-by: Michael Ellerman <mpe@ellerman.id.au>
Fixes: f636c14790ea ("powerpc/pseries: Set or clear security feature flags")
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/platforms/pseries/setup.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -475,13 +475,13 @@ static void init_cpu_char_feature_flags(
* 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);
}