Re: [PATCH][v2] powerpc: Set right value of Speculation_Store_Bypass in /proc/<pid>/status
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2019-11-26 02:28:20
Also in:
lkml
Gustavo Walbon [off-list ref] writes:
The issue has showed the value of status of Speculation_Store_Bypass in the /proc/<pid>/status as `unknown` for PowerPC systems. The patch fix the checking of the mitigation status of Speculation, and can be reported as "not vulnerable", "globally mitigated" or "vulnerable". Link: https://github.com/linuxppc/issues/issues/255 Changelog: Rebase on v5.4-rc8 Signed-off-by: Gustavo Walbon <redacted> --- arch/powerpc/kernel/security.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-)
On further thoughts I don't think this logic (which I suggested) is
right >:(
I commented on the issue:
I think my original suggestion on this was wrong.
Our mitigation is not global, ie. it's a barrier that must be used in
the right location. We have kernel code to insert the barrier on
kernel entry/exit, but that doesn't protect userspace against itself
(ie. sandboxes).
There's no way to express that with the current values as far as I can
see.
I think all we can do for now is:
if stf_enabled_flush_types == STF_BARRIER_NONE:
return PR_SPEC_NOT_AFFECTED // "not vulnerable"
else
return PR_SPEC_ENABLE // "vulnerable"
To express the situation properly we'd need another value, something
like PR_SPEC_MITIGATION_AVAILABLE (??) which says that there is a
mitigation available but it must be used. That still has the problem
that it doesn't tell userspace what the mitigation is, userspace would
have to know.
cheers
quoted hunk ↗ jump to hunk
diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c index 7d4b2080a658..04e566026bbc 100644 --- a/arch/powerpc/kernel/security.c +++ b/arch/powerpc/kernel/security.c@@ -14,7 +14,7 @@ #include <asm/debugfs.h> #include <asm/security_features.h> #include <asm/setup.h> - +#include <linux/prctl.h> u64 powerpc_security_features __read_mostly = SEC_FTR_DEFAULT;@@ -344,6 +344,29 @@ ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute * return sprintf(buf, "Vulnerable\n"); } +static int ssb_prctl_get(struct task_struct *task) +{ + if (stf_barrier) { + if (stf_enabled_flush_types == STF_BARRIER_NONE) + return PR_SPEC_NOT_AFFECTED; + else + return PR_SPEC_DISABLE; + } else + return PR_SPEC_DISABLE_NOEXEC; + + return -EINVAL; +} + +int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which) +{ + switch (which) { + case PR_SPEC_STORE_BYPASS: + return ssb_prctl_get(task); + default: + return -ENODEV; + } +} + #ifdef CONFIG_DEBUG_FS static int stf_barrier_set(void *data, u64 val) {-- 2.19.1