* [PATCH] x86-64/Xen: fix stack switching @ 2018-05-07 11:55 Jan Beulich 2018-05-08 2:38 ` Andy Lutomirski [not found] ` <5AF03EBD02000000000F91D6@prv1-mh.provo.novell.com> 0 siblings, 2 replies; 11+ messages in thread From: Jan Beulich @ 2018-05-07 11:55 UTC (permalink / raw) To: mingo, tglx, hpa Cc: Andy Lutomirski, xen-devel, Boris Ostrovsky, Juergen Gross, linux-kernel While on native entry into the kernel happens on the trampoline stack, PV Xen kernels are being entered with the current thread stack right away. Hence source and destination stacks are identical in that case, and special care is needed. Other than in sync_regs() the copying done on the INT80 path as well as on the NMI path itself isn't NMI / #MC safe, as either of these events occurring in the middle of the stack copying would clobber data on the (source) stack. (Of course, in the NMI case only #MC could break things.) I'm not altering the similar code in interrupt_entry(), as that code path is unreachable when running an PV Xen guest afaict. Signed-off-by: Jan Beulich <jbeulich@suse.com> Cc: stable@kernel.org --- There would certainly have been the option of using alternatives patching, but afaict the patching code isn't NMI / #MC safe, so I'd rather stay away from patching the NMI path. And I thought it would be better to use similar code in both cases. Another option would be to make the Xen case match the native one, by going through the trampoline stack, but to me this would look like extra overhead for no gain. --- arch/x86/entry/entry_64.S | 8 ++++++++ arch/x86/entry/entry_64_compat.S | 8 +++++++- 2 files changed, 15 insertions(+), 1 deletion(-) --- 4.17-rc4/arch/x86/entry/entry_64.S +++ 4.17-rc4-x86_64-stack-switch-Xen/arch/x86/entry/entry_64.S @@ -1399,6 +1399,12 @@ ENTRY(nmi) swapgs cld SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx + + movq PER_CPU_VAR(cpu_current_top_of_stack), %rdx + subq $8, %rdx + xorq %rsp, %rdx + shrq $PAGE_SHIFT, %rdx + jz .Lnmi_keep_stack movq %rsp, %rdx movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp UNWIND_HINT_IRET_REGS base=%rdx offset=8 @@ -1408,6 +1414,8 @@ ENTRY(nmi) pushq 2*8(%rdx) /* pt_regs->cs */ pushq 1*8(%rdx) /* pt_regs->rip */ UNWIND_HINT_IRET_REGS +.Lnmi_keep_stack: + pushq $-1 /* pt_regs->orig_ax */ PUSH_AND_CLEAR_REGS rdx=(%rdx) ENCODE_FRAME_POINTER --- 4.17-rc4/arch/x86/entry/entry_64_compat.S +++ 4.17-rc4-x86_64-stack-switch-Xen/arch/x86/entry/entry_64_compat.S @@ -356,15 +356,21 @@ ENTRY(entry_INT80_compat) /* Need to switch before accessing the thread stack. */ SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi + + movq PER_CPU_VAR(cpu_current_top_of_stack), %rdi + subq $8, %rdi + xorq %rsp, %rdi + shrq $PAGE_SHIFT, %rdi + jz .Lint80_keep_stack movq %rsp, %rdi movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp - pushq 6*8(%rdi) /* regs->ss */ pushq 5*8(%rdi) /* regs->rsp */ pushq 4*8(%rdi) /* regs->eflags */ pushq 3*8(%rdi) /* regs->cs */ pushq 2*8(%rdi) /* regs->ip */ pushq 1*8(%rdi) /* regs->orig_ax */ +.Lint80_keep_stack: pushq (%rdi) /* pt_regs->di */ pushq %rsi /* pt_regs->si */ ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] x86-64/Xen: fix stack switching 2018-05-07 11:55 [PATCH] x86-64/Xen: fix stack switching Jan Beulich @ 2018-05-08 2:38 ` Andy Lutomirski 2018-05-14 10:28 ` Jan Beulich [not found] ` <5AF964B302000078001C26BC@suse.com> [not found] ` <5AF03EBD02000000000F91D6@prv1-mh.provo.novell.com> 1 sibling, 2 replies; 11+ messages in thread From: Andy Lutomirski @ 2018-05-08 2:38 UTC (permalink / raw) To: Jan Beulich Cc: Ingo Molnar, Thomas Gleixner, H. Peter Anvin, Andrew Lutomirski, xen-devel, Boris Ostrovsky, Juergen Gross, LKML On Mon, May 7, 2018 at 5:16 AM Jan Beulich <JBeulich@suse.com> wrote: > While on native entry into the kernel happens on the trampoline stack, > PV Xen kernels are being entered with the current thread stack right > away. Hence source and destination stacks are identical in that case, > and special care is needed. > Other than in sync_regs() the copying done on the INT80 path as well as > on the NMI path itself isn't NMI / #MC safe, as either of these events > occurring in the middle of the stack copying would clobber data on the > (source) stack. (Of course, in the NMI case only #MC could break > things.) I think I'd rather fix this by changing the stack switch code or alternativing around it on non-stack-switching kernels. Or make Xen use a trampoline stack just like native. > I'm not altering the similar code in interrupt_entry(), as that code > path is unreachable when running an PV Xen guest afaict. > Signed-off-by: Jan Beulich <jbeulich@suse.com> > Cc: stable@kernel.org > --- > There would certainly have been the option of using alternatives > patching, but afaict the patching code isn't NMI / #MC safe, so I'd > rather stay away from patching the NMI path. And I thought it would be > better to use similar code in both cases. I would hope we do the patching before we enable any NMIs. > Another option would be to make the Xen case match the native one, by > going through the trampoline stack, but to me this would look like extra > overhead for no gain. Avoiding even more complexity in the nmi code seems like a big gain to me. ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] x86-64/Xen: fix stack switching 2018-05-08 2:38 ` Andy Lutomirski @ 2018-05-14 10:28 ` Jan Beulich [not found] ` <5AF964B302000078001C26BC@suse.com> 1 sibling, 0 replies; 11+ messages in thread From: Jan Beulich @ 2018-05-14 10:28 UTC (permalink / raw) To: Andrew Lutomirski Cc: mingo, tglx, xen-devel, Boris Ostrovsky, Juergen Gross, linux-kernel, hpa >>> On 08.05.18 at 04:38, <luto@kernel.org> wrote: > On Mon, May 7, 2018 at 5:16 AM Jan Beulich <JBeulich@suse.com> wrote: > >> While on native entry into the kernel happens on the trampoline stack, >> PV Xen kernels are being entered with the current thread stack right >> away. Hence source and destination stacks are identical in that case, >> and special care is needed. > >> Other than in sync_regs() the copying done on the INT80 path as well as >> on the NMI path itself isn't NMI / #MC safe, as either of these events >> occurring in the middle of the stack copying would clobber data on the >> (source) stack. (Of course, in the NMI case only #MC could break >> things.) > > I think I'd rather fix this by changing the stack switch code or Well, isn't that what I'm doing in the patch? > alternativing around it on non-stack-switching kernels. Fine with me if that's considered better than adding the conditionals. > Or make Xen use a trampoline stack just like native. Well, as said I'd rather not, unless x86 and Xen maintainers agree that's the way to go. But see below for NMI. >> I'm not altering the similar code in interrupt_entry(), as that code >> path is unreachable when running an PV Xen guest afaict. > >> Signed-off-by: Jan Beulich <jbeulich@suse.com> >> Cc: stable@kernel.org >> --- >> There would certainly have been the option of using alternatives >> patching, but afaict the patching code isn't NMI / #MC safe, so I'd >> rather stay away from patching the NMI path. And I thought it would be >> better to use similar code in both cases. > > I would hope we do the patching before we enable any NMIs. "Enable NMIs"? I don't think they're getting disabled anywhere in the kernel. Perhaps you merely mean ones the kernel sends itself (which I agree would hopefully only be enabled after alternatives patching? >> Another option would be to make the Xen case match the native one, by >> going through the trampoline stack, but to me this would look like extra >> overhead for no gain. > > Avoiding even more complexity in the nmi code seems like a big gain to me. I'm not sure the added conditional is more complexity than making Xen switch to the trampoline stack just to switch back almost immediately. But yes, I could see complexity of the NMI code to be a reason to use different solutions on the NMI and INT80 paths. It's just that I'd like you, the x86 maintainters, and the Xen ones to agree on which solution to use where before I'd send a v2. Jan ^ permalink raw reply [flat|nested] 11+ messages in thread
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* Re: [PATCH] x86-64/Xen: fix stack switching [not found] ` <5AF964B302000078001C26BC@suse.com> @ 2018-05-14 12:08 ` Juergen Gross 0 siblings, 0 replies; 11+ messages in thread From: Juergen Gross @ 2018-05-14 12:08 UTC (permalink / raw) To: Jan Beulich, Andrew Lutomirski Cc: Ingo Molnar, Thomas Gleixner, xen-devel, Boris Ostrovsky, lkml, H. Peter Anvin On 14/05/18 12:28, Jan Beulich wrote: >>>> On 08.05.18 at 04:38, <luto@kernel.org> wrote: >> On Mon, May 7, 2018 at 5:16 AM Jan Beulich <JBeulich@suse.com> wrote: >> >>> While on native entry into the kernel happens on the trampoline stack, >>> PV Xen kernels are being entered with the current thread stack right >>> away. Hence source and destination stacks are identical in that case, >>> and special care is needed. >> >>> Other than in sync_regs() the copying done on the INT80 path as well as >>> on the NMI path itself isn't NMI / #MC safe, as either of these events >>> occurring in the middle of the stack copying would clobber data on the >>> (source) stack. (Of course, in the NMI case only #MC could break >>> things.) >> >> I think I'd rather fix this by changing the stack switch code or > > Well, isn't that what I'm doing in the patch? > >> alternativing around it on non-stack-switching kernels. > > Fine with me if that's considered better than adding the conditionals. > >> Or make Xen use a trampoline stack just like native. > > Well, as said I'd rather not, unless x86 and Xen maintainers agree > that's the way to go. But see below for NMI. I'd prefer not using a trampoline stack, too. > >>> I'm not altering the similar code in interrupt_entry(), as that code >>> path is unreachable when running an PV Xen guest afaict. >> >>> Signed-off-by: Jan Beulich <jbeulich@suse.com> >>> Cc: stable@kernel.org >>> --- >>> There would certainly have been the option of using alternatives >>> patching, but afaict the patching code isn't NMI / #MC safe, so I'd >>> rather stay away from patching the NMI path. And I thought it would be >>> better to use similar code in both cases. >> >> I would hope we do the patching before we enable any NMIs. > > "Enable NMIs"? I don't think they're getting disabled anywhere in the > kernel. Perhaps you merely mean ones the kernel sends itself (which > I agree would hopefully only be enabled after alternatives patching? > >>> Another option would be to make the Xen case match the native one, by >>> going through the trampoline stack, but to me this would look like extra >>> overhead for no gain. >> >> Avoiding even more complexity in the nmi code seems like a big gain to me. > > I'm not sure the added conditional is more complexity than making Xen > switch to the trampoline stack just to switch back almost immediately. I agree. > But yes, I could see complexity of the NMI code to be a reason to use > different solutions on the NMI and INT80 paths. It's just that I'd like > you, the x86 maintainters, and the Xen ones to agree on which solution > to use where before I'd send a v2. With my Xen maintainer hat on I'd prefer Jan's current solution. Juergen ^ permalink raw reply [flat|nested] 11+ messages in thread
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* [PATCH v2] x86-64/Xen: fix stack switching [not found] ` <5AF03EBD02000078001FE590@prv1-mh.provo.novell.com> @ 2018-11-21 10:10 ` Jan Beulich 2018-11-21 15:24 ` Andy Lutomirski 2019-01-15 16:58 ` [PATCH v3] " Jan Beulich 1 sibling, 1 reply; 11+ messages in thread From: Jan Beulich @ 2018-11-21 10:10 UTC (permalink / raw) To: mingo, tglx, hpa Cc: Andrew Lutomirski, xen-devel, Boris Ostrovsky, Juergen Gross, linux-kernel While in the native case entry into the kernel happens on the trampoline stack, PV Xen kernels get entered with the current thread stack right away. Hence source and destination stacks are identical in that case, and special care is needed. Other than in sync_regs() the copying done on the INT80 path as well as on the NMI path itself isn't NMI / #MC safe, as either of these events occurring in the middle of the stack copying would clobber data on the (source) stack. (Of course, in the NMI case only #MC could break things.) I'm not altering the similar code in interrupt_entry(), as that code path is unreachable afaict when running PV Xen guests. Fixes: 7f2590a110b837af5679d08fc25c6227c5a8c497 Signed-off-by: Jan Beulich <jbeulich@suse.com> Cc: stable@kernel.org --- v2: Correct placement of .Lint80_keep_stack label. --- arch/x86/entry/entry_64.S | 8 ++++++++ arch/x86/entry/entry_64_compat.S | 10 ++++++++-- 2 files changed, 16 insertions(+), 2 deletions(-) --- 4.20-rc3/arch/x86/entry/entry_64.S +++ 4.20-rc3-x86_64-stack-switch-Xen/arch/x86/entry/entry_64.S @@ -1380,6 +1380,12 @@ ENTRY(nmi) swapgs cld SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx + + movq PER_CPU_VAR(cpu_current_top_of_stack), %rdx + subq $8, %rdx + xorq %rsp, %rdx + shrq $PAGE_SHIFT, %rdx + jz .Lnmi_keep_stack movq %rsp, %rdx movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp UNWIND_HINT_IRET_REGS base=%rdx offset=8 @@ -1389,6 +1395,8 @@ ENTRY(nmi) pushq 2*8(%rdx) /* pt_regs->cs */ pushq 1*8(%rdx) /* pt_regs->rip */ UNWIND_HINT_IRET_REGS +.Lnmi_keep_stack: + pushq $-1 /* pt_regs->orig_ax */ PUSH_AND_CLEAR_REGS rdx=(%rdx) ENCODE_FRAME_POINTER --- 4.20-rc3/arch/x86/entry/entry_64_compat.S +++ 4.20-rc3-x86_64-stack-switch-Xen/arch/x86/entry/entry_64_compat.S @@ -361,17 +361,23 @@ ENTRY(entry_INT80_compat) /* Need to switch before accessing the thread stack. */ SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi + + movq PER_CPU_VAR(cpu_current_top_of_stack), %rdi + subq $8, %rdi + xorq %rsp, %rdi + shrq $PAGE_SHIFT, %rdi + jz .Lint80_keep_stack movq %rsp, %rdi movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp - pushq 6*8(%rdi) /* regs->ss */ pushq 5*8(%rdi) /* regs->rsp */ pushq 4*8(%rdi) /* regs->eflags */ pushq 3*8(%rdi) /* regs->cs */ pushq 2*8(%rdi) /* regs->ip */ pushq 1*8(%rdi) /* regs->orig_ax */ - pushq (%rdi) /* pt_regs->di */ +.Lint80_keep_stack: + pushq %rsi /* pt_regs->si */ xorl %esi, %esi /* nospec si */ pushq %rdx /* pt_regs->dx */ ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v2] x86-64/Xen: fix stack switching 2018-11-21 10:10 ` [PATCH v2] " Jan Beulich @ 2018-11-21 15:24 ` Andy Lutomirski 2018-11-22 8:07 ` Jan Beulich 0 siblings, 1 reply; 11+ messages in thread From: Andy Lutomirski @ 2018-11-21 15:24 UTC (permalink / raw) To: Jan Beulich Cc: Ingo Molnar, Thomas Gleixner, H. Peter Anvin, Andrew Lutomirski, xen-devel, Boris Ostrovsky, Juergen Gross, LKML On Wed, Nov 21, 2018 at 2:10 AM Jan Beulich <JBeulich@suse.com> wrote: > > While in the native case entry into the kernel happens on the trampoline > stack, PV Xen kernels get entered with the current thread stack right > away. Hence source and destination stacks are identical in that case, > and special care is needed. > > Other than in sync_regs() the copying done on the INT80 path as well as > on the NMI path itself isn't NMI / #MC safe, as either of these events > occurring in the middle of the stack copying would clobber data on the > (source) stack. (Of course, in the NMI case only #MC could break > things.) > > I'm not altering the similar code in interrupt_entry(), as that code > path is unreachable afaict when running PV Xen guests. > > Fixes: 7f2590a110b837af5679d08fc25c6227c5a8c497 > Signed-off-by: Jan Beulich <jbeulich@suse.com> > Cc: stable@kernel.org > --- > v2: Correct placement of .Lint80_keep_stack label. > --- > arch/x86/entry/entry_64.S | 8 ++++++++ > arch/x86/entry/entry_64_compat.S | 10 ++++++++-- > 2 files changed, 16 insertions(+), 2 deletions(-) > > --- 4.20-rc3/arch/x86/entry/entry_64.S > +++ 4.20-rc3-x86_64-stack-switch-Xen/arch/x86/entry/entry_64.S > @@ -1380,6 +1380,12 @@ ENTRY(nmi) > swapgs > cld > SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx > + > + movq PER_CPU_VAR(cpu_current_top_of_stack), %rdx > + subq $8, %rdx > + xorq %rsp, %rdx > + shrq $PAGE_SHIFT, %rdx > + jz .Lnmi_keep_stack This code shouldn't even be reachable on Xen: commit 43e4111086a70c78bedb6ad990bee97f17b27a6e Author: Juergen Gross <jgross@suse.com> Date: Thu Nov 2 00:59:07 2017 -0700 xen, x86/entry/64: Add xen NMI trap entry Instead of trying to execute any NMI via the bare metal's NMI trap handler use a Xen specific one for PV domains, like we do for e.g. debug traps. As in a PV domain the NMI is handled via the normal kernel stack this is the correct thing to do. This will enable us to get rid of the very fragile and questionable dependencies between the bare metal NMI handler and Xen assumptions believed to be broken anyway. > movq %rsp, %rdx > movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp > UNWIND_HINT_IRET_REGS base=%rdx offset=8 > @@ -1389,6 +1395,8 @@ ENTRY(nmi) > pushq 2*8(%rdx) /* pt_regs->cs */ > pushq 1*8(%rdx) /* pt_regs->rip */ > UNWIND_HINT_IRET_REGS > +.Lnmi_keep_stack: > + > pushq $-1 /* pt_regs->orig_ax */ > PUSH_AND_CLEAR_REGS rdx=(%rdx) > ENCODE_FRAME_POINTER > --- 4.20-rc3/arch/x86/entry/entry_64_compat.S > +++ 4.20-rc3-x86_64-stack-switch-Xen/arch/x86/entry/entry_64_compat.S > @@ -361,17 +361,23 @@ ENTRY(entry_INT80_compat) > > /* Need to switch before accessing the thread stack. */ > SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi > + > + movq PER_CPU_VAR(cpu_current_top_of_stack), %rdi > + subq $8, %rdi > + xorq %rsp, %rdi > + shrq $PAGE_SHIFT, %rdi > + jz .Lint80_keep_stack This comparison is IMO the wrong test entirely. How about something like: /* On Xen PV, entry_INT80_compat is called on the thread stack, so rewinding to the top of the thread stack would allow an NMI to overwrite the hardware frame before we copy it. */ ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v2] x86-64/Xen: fix stack switching 2018-11-21 15:24 ` Andy Lutomirski @ 2018-11-22 8:07 ` Jan Beulich 0 siblings, 0 replies; 11+ messages in thread From: Jan Beulich @ 2018-11-22 8:07 UTC (permalink / raw) To: Andrew Lutomirski Cc: mingo, tglx, xen-devel, Boris Ostrovsky, Juergen Gross, linux-kernel, hpa >>> On 21.11.18 at 16:24, <luto@kernel.org> wrote: > On Wed, Nov 21, 2018 at 2:10 AM Jan Beulich <JBeulich@suse.com> wrote: >> --- 4.20-rc3/arch/x86/entry/entry_64.S >> +++ 4.20-rc3-x86_64-stack-switch-Xen/arch/x86/entry/entry_64.S >> @@ -1380,6 +1380,12 @@ ENTRY(nmi) >> swapgs >> cld >> SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx >> + >> + movq PER_CPU_VAR(cpu_current_top_of_stack), %rdx >> + subq $8, %rdx >> + xorq %rsp, %rdx >> + shrq $PAGE_SHIFT, %rdx >> + jz .Lnmi_keep_stack > > This code shouldn't even be reachable on Xen: > > commit 43e4111086a70c78bedb6ad990bee97f17b27a6e > Author: Juergen Gross <jgross@suse.com> > Date: Thu Nov 2 00:59:07 2017 -0700 > > xen, x86/entry/64: Add xen NMI trap entry > > Instead of trying to execute any NMI via the bare metal's NMI trap > handler use a Xen specific one for PV domains, like we do for e.g. > debug traps. As in a PV domain the NMI is handled via the normal > kernel stack this is the correct thing to do. > > This will enable us to get rid of the very fragile and questionable > dependencies between the bare metal NMI handler and Xen assumptions > believed to be broken anyway. Oh, I didn't notice this. The beginnings of the patch here pre-date this, though, and then I didn't notice the addition. Thanks for pointing this out. >> --- 4.20-rc3/arch/x86/entry/entry_64_compat.S >> +++ 4.20-rc3-x86_64-stack-switch-Xen/arch/x86/entry/entry_64_compat.S >> @@ -361,17 +361,23 @@ ENTRY(entry_INT80_compat) >> >> /* Need to switch before accessing the thread stack. */ >> SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi >> + >> + movq PER_CPU_VAR(cpu_current_top_of_stack), %rdi >> + subq $8, %rdi >> + xorq %rsp, %rdi >> + shrq $PAGE_SHIFT, %rdi >> + jz .Lint80_keep_stack > > This comparison is IMO the wrong test entirely. How about something like: > > /* On Xen PV, entry_INT80_compat is called on the thread stack, so > rewinding to the top of the thread stack would allow an NMI to > overwrite the hardware frame before we copy it. */ > ALTERNATIVE "", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV Indeed I had noted this as an alternative option in v1, but didn't get respective feedback. If that's the preferred route, I'll certainly switch. Jan ^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v3] x86-64/Xen: fix stack switching [not found] ` <5AF03EBD02000078001FE590@prv1-mh.provo.novell.com> 2018-11-21 10:10 ` [PATCH v2] " Jan Beulich @ 2019-01-15 16:58 ` Jan Beulich 2019-01-17 0:09 ` Andy Lutomirski 2019-01-17 23:42 ` [tip:x86/urgent] x86/entry/64/compat: Fix stack switching for XEN PV tip-bot for Jan Beulich 1 sibling, 2 replies; 11+ messages in thread From: Jan Beulich @ 2019-01-15 16:58 UTC (permalink / raw) To: mingo, tglx, hpa Cc: Andrew Lutomirski, xen-devel, Boris Ostrovsky, Juergen Gross, linux-kernel While in the native case entry into the kernel happens on the trampoline stack, PV Xen kernels get entered with the current thread stack right away. Hence source and destination stacks are identical in that case, and special care is needed. Other than in sync_regs() the copying done on the INT80 path isn't NMI / #MC safe, as either of these events occurring in the middle of the stack copying would clobber data on the (source) stack. I'm not altering the similar code in interrupt_entry() and nmi(), as those code paths are unreachable afaict when running PV Xen guests. Fixes: 7f2590a110b837af5679d08fc25c6227c5a8c497 Signed-off-by: Jan Beulich <jbeulich@suse.com> Cc: stable@kernel.org --- v3: Drop NMI path change. Use ALTERNATIVE. v2: Correct placement of .Lint80_keep_stack label. --- arch/x86/entry/entry_64_compat.S | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- 5.0-rc2/arch/x86/entry/entry_64_compat.S +++ 5.0-rc2-x86_64-stack-switch-Xen/arch/x86/entry/entry_64_compat.S @@ -361,7 +361,8 @@ ENTRY(entry_INT80_compat) /* Need to switch before accessing the thread stack. */ SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi - movq %rsp, %rdi + /* In the Xen PV case we already run on the thread stack. */ + ALTERNATIVE "movq %rsp, %rdi", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp pushq 6*8(%rdi) /* regs->ss */ @@ -370,8 +371,9 @@ ENTRY(entry_INT80_compat) pushq 3*8(%rdi) /* regs->cs */ pushq 2*8(%rdi) /* regs->ip */ pushq 1*8(%rdi) /* regs->orig_ax */ - pushq (%rdi) /* pt_regs->di */ +.Lint80_keep_stack: + pushq %rsi /* pt_regs->si */ xorl %esi, %esi /* nospec si */ pushq %rdx /* pt_regs->dx */ ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH v3] x86-64/Xen: fix stack switching 2019-01-15 16:58 ` [PATCH v3] " Jan Beulich @ 2019-01-17 0:09 ` Andy Lutomirski 2019-01-17 23:42 ` [tip:x86/urgent] x86/entry/64/compat: Fix stack switching for XEN PV tip-bot for Jan Beulich 1 sibling, 0 replies; 11+ messages in thread From: Andy Lutomirski @ 2019-01-17 0:09 UTC (permalink / raw) To: Jan Beulich Cc: Ingo Molnar, Thomas Gleixner, H. Peter Anvin, Andrew Lutomirski, xen-devel, Boris Ostrovsky, Juergen Gross, LKML On Tue, Jan 15, 2019 at 8:58 AM Jan Beulich <JBeulich@suse.com> wrote: > > While in the native case entry into the kernel happens on the trampoline > stack, PV Xen kernels get entered with the current thread stack right > away. Hence source and destination stacks are identical in that case, > and special care is needed. > > Other than in sync_regs() the copying done on the INT80 path isn't > NMI / #MC safe, as either of these events occurring in the middle of the > stack copying would clobber data on the (source) stack. > > I'm not altering the similar code in interrupt_entry() and nmi(), as > those code paths are unreachable afaict when running PV Xen guests. Acked-by: Andy Lutomirski <luto@kernel.org> ^ permalink raw reply [flat|nested] 11+ messages in thread
* [tip:x86/urgent] x86/entry/64/compat: Fix stack switching for XEN PV 2019-01-15 16:58 ` [PATCH v3] " Jan Beulich 2019-01-17 0:09 ` Andy Lutomirski @ 2019-01-17 23:42 ` tip-bot for Jan Beulich 1 sibling, 0 replies; 11+ messages in thread From: tip-bot for Jan Beulich @ 2019-01-17 23:42 UTC (permalink / raw) To: linux-tip-commits Cc: luto, linux-kernel, jbeulich, mingo, boris.ostrovsky, hpa, JBeulich, tglx, jgross Commit-ID: fc24d75a7f91837d7918e40719575951820b2b8f Gitweb: https://git.kernel.org/tip/fc24d75a7f91837d7918e40719575951820b2b8f Author: Jan Beulich <JBeulich@suse.com> AuthorDate: Tue, 15 Jan 2019 09:58:16 -0700 Committer: Thomas Gleixner <tglx@linutronix.de> CommitDate: Fri, 18 Jan 2019 00:39:33 +0100 x86/entry/64/compat: Fix stack switching for XEN PV While in the native case entry into the kernel happens on the trampoline stack, PV Xen kernels get entered with the current thread stack right away. Hence source and destination stacks are identical in that case, and special care is needed. Other than in sync_regs() the copying done on the INT80 path isn't NMI / #MC safe, as either of these events occurring in the middle of the stack copying would clobber data on the (source) stack. There is similar code in interrupt_entry() and nmi(), but there is no fixup required because those code paths are unreachable in XEN PV guests. [ tglx: Sanitized subject, changelog, Fixes tag and stable mail address. Sigh ] Fixes: 7f2590a110b8 ("x86/entry/64: Use a per-CPU trampoline stack for IDT entries") Signed-off-by: Jan Beulich <jbeulich@suse.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Juergen Gross <jgross@suse.com> Acked-by: Andy Lutomirski <luto@kernel.org> Cc: Peter Anvin <hpa@zytor.com> Cc: xen-devel@lists.xenproject.org> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/5C3E1128020000780020DFAD@prv1-mh.provo.novell.com --- arch/x86/entry/entry_64_compat.S | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index 8eaf8952c408..39913770a44d 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -361,7 +361,8 @@ ENTRY(entry_INT80_compat) /* Need to switch before accessing the thread stack. */ SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi - movq %rsp, %rdi + /* In the Xen PV case we already run on the thread stack. */ + ALTERNATIVE "movq %rsp, %rdi", "jmp .Lint80_keep_stack", X86_FEATURE_XENPV movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp pushq 6*8(%rdi) /* regs->ss */ @@ -370,8 +371,9 @@ ENTRY(entry_INT80_compat) pushq 3*8(%rdi) /* regs->cs */ pushq 2*8(%rdi) /* regs->ip */ pushq 1*8(%rdi) /* regs->orig_ax */ - pushq (%rdi) /* pt_regs->di */ +.Lint80_keep_stack: + pushq %rsi /* pt_regs->si */ xorl %esi, %esi /* nospec si */ pushq %rdx /* pt_regs->dx */ ^ permalink raw reply related [flat|nested] 11+ messages in thread
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* Re: [PATCH v3] x86-64/Xen: fix stack switching [not found] ` <5C3E1128020000780020DFAD@suse.com> @ 2019-01-16 11:51 ` Juergen Gross 0 siblings, 0 replies; 11+ messages in thread From: Juergen Gross @ 2019-01-16 11:51 UTC (permalink / raw) To: Jan Beulich, Ingo Molnar, Thomas Gleixner, H. Peter Anvin Cc: Andrew Lutomirski, xen-devel, Boris Ostrovsky, lkml On 15/01/2019 17:58, Jan Beulich wrote: > While in the native case entry into the kernel happens on the trampoline > stack, PV Xen kernels get entered with the current thread stack right > away. Hence source and destination stacks are identical in that case, > and special care is needed. > > Other than in sync_regs() the copying done on the INT80 path isn't > NMI / #MC safe, as either of these events occurring in the middle of the > stack copying would clobber data on the (source) stack. > > I'm not altering the similar code in interrupt_entry() and nmi(), as > those code paths are unreachable afaict when running PV Xen guests. > > Fixes: 7f2590a110b837af5679d08fc25c6227c5a8c497 > Signed-off-by: Jan Beulich <jbeulich@suse.com> > Cc: stable@kernel.org Reviewed-by: Juergen Gross <jgross@suse.com> Juergen ^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2019-01-17 23:43 UTC | newest] Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2018-05-07 11:55 [PATCH] x86-64/Xen: fix stack switching Jan Beulich 2018-05-08 2:38 ` Andy Lutomirski 2018-05-14 10:28 ` Jan Beulich [not found] ` <5AF964B302000078001C26BC@suse.com> 2018-05-14 12:08 ` Juergen Gross [not found] ` <5AF03EBD02000000000F91D6@prv1-mh.provo.novell.com> [not found] ` <5AF03EBD02000078001FE590@prv1-mh.provo.novell.com> 2018-11-21 10:10 ` [PATCH v2] " Jan Beulich 2018-11-21 15:24 ` Andy Lutomirski 2018-11-22 8:07 ` Jan Beulich 2019-01-15 16:58 ` [PATCH v3] " Jan Beulich 2019-01-17 0:09 ` Andy Lutomirski 2019-01-17 23:42 ` [tip:x86/urgent] x86/entry/64/compat: Fix stack switching for XEN PV tip-bot for Jan Beulich [not found] <5AF03EBD02000078001C1303@suse.com> [not found] ` <5AF03EBD02000000000F91D6@suse.com> [not found] ` <5AF03EBD02000078001FE590@suse.com> [not found] ` <5C3E1128020000780020DFAD@suse.com> 2019-01-16 11:51 ` [PATCH v3] x86-64/Xen: fix stack switching Juergen Gross
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