| Message ID | 20190505221048.28212-1-cmr@informatik.wtf (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | powerpc/64s: support nospectre_v2 cmdline option | expand |
On 6/5/19 8:10 am, Christopher M. Riedl wrote: > Add support for disabling the kernel implemented spectre v2 mitigation > (count cache flush on context switch) via the nospectre_v2 cmdline > option. > > Suggested-by: Michael Ellerman <mpe@ellerman.id.au> > Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf> > --- > > arch/powerpc/kernel/security.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c > index b33bafb8fcea..f7c34745cd0f 100644 > --- a/arch/powerpc/kernel/security.c > +++ b/arch/powerpc/kernel/security.c > @@ -28,7 +28,7 @@ static enum count_cache_flush_type count_cache_flush_type = COUNT_CACHE_FLUSH_NO > bool barrier_nospec_enabled; > static bool no_nospec; > static bool btb_flush_enabled; > -#ifdef CONFIG_PPC_FSL_BOOK3E > +#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64) > static bool no_spectrev2; > #endif > > @@ -106,7 +106,7 @@ static __init int barrier_nospec_debugfs_init(void) > device_initcall(barrier_nospec_debugfs_init); > #endif /* CONFIG_DEBUG_FS */ > > -#ifdef CONFIG_PPC_FSL_BOOK3E > +#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64) > static int __init handle_nospectre_v2(char *p) > { > no_spectrev2 = true; > @@ -114,6 +114,9 @@ static int __init handle_nospectre_v2(char *p) > return 0; > } > early_param("nospectre_v2", handle_nospectre_v2); > +#endif /* CONFIG_PPC_FSL_BOOK3E || CONFIG_PPC_BOOK3S_64 */ > + > +#ifdef CONFIG_PPC_FSL_BOOK3E > void setup_spectre_v2(void) > { > if (no_spectrev2) > @@ -391,6 +394,13 @@ static void toggle_count_cache_flush(bool enable) > > void setup_count_cache_flush(void) > { > + if (no_spectrev2) { > + if (security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED) > + || security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED)) > + pr_warn("Spectre v2 mitigations not under software control, can't disable\n"); If one of those ftrs is set, what's the impact of not calling toggle_count_cache_flush()? > + return; > + } > + > toggle_count_cache_flush(true); > } > >
> On May 5, 2019 at 9:32 PM Andrew Donnellan <ajd@linux.ibm.com> wrote: > > > On 6/5/19 8:10 am, Christopher M. Riedl wrote: > > Add support for disabling the kernel implemented spectre v2 mitigation > > (count cache flush on context switch) via the nospectre_v2 cmdline > > option. > > > > Suggested-by: Michael Ellerman <mpe@ellerman.id.au> > > Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf> > > --- > > > > arch/powerpc/kernel/security.c | 14 ++++++++++++-- > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c > > index b33bafb8fcea..f7c34745cd0f 100644 > > --- a/arch/powerpc/kernel/security.c > > +++ b/arch/powerpc/kernel/security.c > > @@ -28,7 +28,7 @@ static enum count_cache_flush_type count_cache_flush_type = COUNT_CACHE_FLUSH_NO > > bool barrier_nospec_enabled; > > static bool no_nospec; > > static bool btb_flush_enabled; > > -#ifdef CONFIG_PPC_FSL_BOOK3E > > +#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64) > > static bool no_spectrev2; > > #endif > > > > @@ -106,7 +106,7 @@ static __init int barrier_nospec_debugfs_init(void) > > device_initcall(barrier_nospec_debugfs_init); > > #endif /* CONFIG_DEBUG_FS */ > > > > -#ifdef CONFIG_PPC_FSL_BOOK3E > > +#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64) > > static int __init handle_nospectre_v2(char *p) > > { > > no_spectrev2 = true; > > @@ -114,6 +114,9 @@ static int __init handle_nospectre_v2(char *p) > > return 0; > > } > > early_param("nospectre_v2", handle_nospectre_v2); > > +#endif /* CONFIG_PPC_FSL_BOOK3E || CONFIG_PPC_BOOK3S_64 */ > > + > > +#ifdef CONFIG_PPC_FSL_BOOK3E > > void setup_spectre_v2(void) > > { > > if (no_spectrev2) > > @@ -391,6 +394,13 @@ static void toggle_count_cache_flush(bool enable) > > > > void setup_count_cache_flush(void) > > { > > + if (no_spectrev2) { > > + if (security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED) > > + || security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED)) > > + pr_warn("Spectre v2 mitigations not under software control, can't disable\n"); > > If one of those ftrs is set, what's the impact of not calling > toggle_count_cache_flush()? > The patchsite/callsite (kernel/entry_64.S:597) for flush_count_cache inside _switch remains a nop. Disassembly of vmlinux after build: c00000000000e260: 00 00 23 f8 std r1,0(r3) c00000000000e264: 00 00 00 60 nop c00000000000e268: 00 60 c0 3c lis r6,24576 Disassembly (xmon) after boot/during runtime in qemu: c00000000000e260 f8230000 std r1,0(r3) c00000000000e264 4bffdb7d bl c00000000000bde0 # flush_count_cache+0x0/0x2420 c00000000000e268 3cc06000 lis r6,24576 Disassembly (xmon) after boot/during runtime in qemu w/ nospectre_v2: c00000000000e260 f8230000 std r1,0(r3) c00000000000e264 60000000 nop c00000000000e268 3cc06000 lis r6,24576 toggle_count_cache_flush() well uhh "toggles" the patchsite to either contain a branch to the flush procedure or a nop. > > + return; > > + } > > + > > toggle_count_cache_flush(true); > > } > > > > > > -- > Andrew Donnellan OzLabs, ADL Canberra > ajd@linux.ibm.com IBM Australia Limited >
Christopher M Riedl <cmr@informatik.wtf> writes: >> On May 5, 2019 at 9:32 PM Andrew Donnellan <ajd@linux.ibm.com> wrote: >> On 6/5/19 8:10 am, Christopher M. Riedl wrote: >> > Add support for disabling the kernel implemented spectre v2 mitigation >> > (count cache flush on context switch) via the nospectre_v2 cmdline >> > option. >> > >> > Suggested-by: Michael Ellerman <mpe@ellerman.id.au> >> > Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf> >> > >> > diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c >> > index b33bafb8fcea..f7c34745cd0f 100644 >> > --- a/arch/powerpc/kernel/security.c >> > +++ b/arch/powerpc/kernel/security.c >> > @@ -391,6 +394,13 @@ static void toggle_count_cache_flush(bool enable) >> > >> > void setup_count_cache_flush(void) >> > { >> > + if (no_spectrev2) { >> > + if (security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED) >> > + || security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED)) >> > + pr_warn("Spectre v2 mitigations not under software control, can't disable\n"); >> >> If one of those ftrs is set, what's the impact of not calling >> toggle_count_cache_flush()? >> > > The patchsite/callsite (kernel/entry_64.S:597) for flush_count_cache > inside _switch remains a nop. > > Disassembly of vmlinux after build: > c00000000000e260: 00 00 23 f8 std r1,0(r3) > c00000000000e264: 00 00 00 60 nop > c00000000000e268: 00 60 c0 3c lis r6,24576 > > Disassembly (xmon) after boot/during runtime in qemu: > c00000000000e260 f8230000 std r1,0(r3) > c00000000000e264 4bffdb7d bl c00000000000bde0 # flush_count_cache+0x0/0x2420 > c00000000000e268 3cc06000 lis r6,24576 > > Disassembly (xmon) after boot/during runtime in qemu w/ nospectre_v2: > c00000000000e260 f8230000 std r1,0(r3) > c00000000000e264 60000000 nop > c00000000000e268 3cc06000 lis r6,24576 Yes you're right, in this case the initial state is deactivated. > toggle_count_cache_flush() well uhh "toggles" the patchsite to either > contain a branch to the flush procedure or a nop. Sort of. It doesn't actually know the initial state, so calling it at boot with false will still nop out the nops. I think I'd probably prefer it if we still call toggle_count_cache_flush(false) when no_spectrev2 is true. The main reason being that it means we'll print to dmesg, but it would also avoid problems if we ever change the initial state of the count cache flush. cheers
> On May 6, 2019 at 9:29 PM Michael Ellerman <mpe@ellerman.id.au> wrote: > > > Christopher M Riedl <cmr@informatik.wtf> writes: > >> On May 5, 2019 at 9:32 PM Andrew Donnellan <ajd@linux.ibm.com> wrote: > >> On 6/5/19 8:10 am, Christopher M. Riedl wrote: > >> > Add support for disabling the kernel implemented spectre v2 mitigation > >> > (count cache flush on context switch) via the nospectre_v2 cmdline > >> > option. > >> > > >> > Suggested-by: Michael Ellerman <mpe@ellerman.id.au> > >> > Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf> > >> > > >> > diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c > >> > index b33bafb8fcea..f7c34745cd0f 100644 > >> > --- a/arch/powerpc/kernel/security.c > >> > +++ b/arch/powerpc/kernel/security.c > >> > @@ -391,6 +394,13 @@ static void toggle_count_cache_flush(bool enable) > >> > > >> > void setup_count_cache_flush(void) > >> > { > >> > + if (no_spectrev2) { > >> > + if (security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED) > >> > + || security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED)) > >> > + pr_warn("Spectre v2 mitigations not under software control, can't disable\n"); > >> > >> If one of those ftrs is set, what's the impact of not calling > >> toggle_count_cache_flush()? > >> > > > > The patchsite/callsite (kernel/entry_64.S:597) for flush_count_cache > > inside _switch remains a nop. > > > > Disassembly of vmlinux after build: > > c00000000000e260: 00 00 23 f8 std r1,0(r3) > > c00000000000e264: 00 00 00 60 nop > > c00000000000e268: 00 60 c0 3c lis r6,24576 > > > > Disassembly (xmon) after boot/during runtime in qemu: > > c00000000000e260 f8230000 std r1,0(r3) > > c00000000000e264 4bffdb7d bl c00000000000bde0 # flush_count_cache+0x0/0x2420 > > c00000000000e268 3cc06000 lis r6,24576 > > > > Disassembly (xmon) after boot/during runtime in qemu w/ nospectre_v2: > > c00000000000e260 f8230000 std r1,0(r3) > > c00000000000e264 60000000 nop > > c00000000000e268 3cc06000 lis r6,24576 > > Yes you're right, in this case the initial state is deactivated. > > > toggle_count_cache_flush() well uhh "toggles" the patchsite to either > > contain a branch to the flush procedure or a nop. > > Sort of. It doesn't actually know the initial state, so calling it at > boot with false will still nop out the nops. > > I think I'd probably prefer it if we still call > toggle_count_cache_flush(false) when no_spectrev2 is true. The main > reason being that it means we'll print to dmesg, but it would also avoid > problems if we ever change the initial state of the count cache flush. > > cheers Sounds good, I will add this to the next version. Thanks!
diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c index b33bafb8fcea..f7c34745cd0f 100644 --- a/arch/powerpc/kernel/security.c +++ b/arch/powerpc/kernel/security.c @@ -28,7 +28,7 @@ static enum count_cache_flush_type count_cache_flush_type = COUNT_CACHE_FLUSH_NO bool barrier_nospec_enabled; static bool no_nospec; static bool btb_flush_enabled; -#ifdef CONFIG_PPC_FSL_BOOK3E +#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64) static bool no_spectrev2; #endif @@ -106,7 +106,7 @@ static __init int barrier_nospec_debugfs_init(void) device_initcall(barrier_nospec_debugfs_init); #endif /* CONFIG_DEBUG_FS */ -#ifdef CONFIG_PPC_FSL_BOOK3E +#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64) static int __init handle_nospectre_v2(char *p) { no_spectrev2 = true; @@ -114,6 +114,9 @@ static int __init handle_nospectre_v2(char *p) return 0; } early_param("nospectre_v2", handle_nospectre_v2); +#endif /* CONFIG_PPC_FSL_BOOK3E || CONFIG_PPC_BOOK3S_64 */ + +#ifdef CONFIG_PPC_FSL_BOOK3E void setup_spectre_v2(void) { if (no_spectrev2) @@ -391,6 +394,13 @@ static void toggle_count_cache_flush(bool enable) void setup_count_cache_flush(void) { + if (no_spectrev2) { + if (security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED) + || security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED)) + pr_warn("Spectre v2 mitigations not under software control, can't disable\n"); + return; + } + toggle_count_cache_flush(true); }
Add support for disabling the kernel implemented spectre v2 mitigation (count cache flush on context switch) via the nospectre_v2 cmdline option. Suggested-by: Michael Ellerman <mpe@ellerman.id.au> Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf> --- reference: https://github.com/linuxppc/issues/issues/236 arch/powerpc/kernel/security.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)