LinuxLists.cc - kexec broken with STACKLEAK enabled

2019-09-23 16:04:26

Subject: kexec broken with STACKLEAK enabled

Hi, since commit b059f801a937 (x86/purgatory: Use CFLAGS_REMOVE rather
than reset KBUILD_CFLAGS) kexec is broken if GCC_PLUGIN_STACKLEAK is
enabled, as the purgatory contains undefined references to
stackleak_track_stack.

Attempting to load a kexec kernel results in an error:

kexec: Undefined symbol: stackleak_track_stack
kexec-bzImage64: Loading purgatory failed

Adding $(DISABLE_STACKLEAK_PLUGIN) to PURGATORY_CFLAGS in
arch/x86/purgatory/Makefile fixes this.

Not sure if that's the best fix or if other architectures also require a
similar one.

Thanks.

2019-09-25 16:20:59

by Nick Desaulniers

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Subject: Re: kexec broken with STACKLEAK enabled

On Sun, Sep 22, 2019 at 10:32 AM Arvind Sankar <[email protected]> wrote:
>
> Hi, since commit b059f801a937 (x86/purgatory: Use CFLAGS_REMOVE rather
> than reset KBUILD_CFLAGS) kexec is broken if GCC_PLUGIN_STACKLEAK is
> enabled, as the purgatory contains undefined references to
> stackleak_track_stack.
>
> Attempting to load a kexec kernel results in an error:
>
> kexec: Undefined symbol: stackleak_track_stack
> kexec-bzImage64: Loading purgatory failed
>
> Adding $(DISABLE_STACKLEAK_PLUGIN) to PURGATORY_CFLAGS in
> arch/x86/purgatory/Makefile fixes this.

Hi Arvind,
Thanks for the report. That sounds like a straightforward fix. Would
you like to send a patch for that? I'd be happy to help review it.

>
> Not sure if that's the best fix or if other architectures also require a
> similar one.

The commit you reference should be x86 only.
--
Thanks,
~Nick Desaulniers

2019-09-25 16:49:33

by Arvind Sankar

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Subject: [PATCH] x86/purgatory: Add $(DISABLE_STACKLEAK_PLUGIN)

Since commit b059f801a937 ("x86/purgatory: Use CFLAGS_REMOVE rather than
reset KBUILD_CFLAGS") kexec breaks is GCC_PLUGIN_STACKLEAK is enabled, as
the purgatory contains undefined references to stackleak_track_stack.
Attempting to load a kexec kernel results in:
kexec: Undefined symbol: stackleak_track_stack
kexec-bzImage64: Loading purgatory failed

Fix this by disabling the stackleak plugin for purgatory.

Fixes: b059f801a937 ("x86/purgatory: Use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS")
Signed-off-by: Arvind Sankar <[email protected]>
---
arch/x86/purgatory/Makefile | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 527749066d31..fb4ee5444379 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -25,6 +25,7 @@ KCOV_INSTRUMENT := n

PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
+PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN)

# Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
# in turn leaves some undefined symbols like __fentry__ in purgatory and not
--
2.21.0

2019-09-25 16:53:38

by Nick Desaulniers

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Subject: Re: [PATCH] x86/purgatory: Add $(DISABLE_STACKLEAK_PLUGIN)

On Mon, Sep 23, 2019 at 10:17 AM Arvind Sankar <[email protected]> wrote:
>
> Since commit b059f801a937 ("x86/purgatory: Use CFLAGS_REMOVE rather than
> reset KBUILD_CFLAGS") kexec breaks is GCC_PLUGIN_STACKLEAK is enabled, as
> the purgatory contains undefined references to stackleak_track_stack.
> Attempting to load a kexec kernel results in:
> kexec: Undefined symbol: stackleak_track_stack
> kexec-bzImage64: Loading purgatory failed
>
> Fix this by disabling the stackleak plugin for purgatory.
>
> Fixes: b059f801a937 ("x86/purgatory: Use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS")
> Signed-off-by: Arvind Sankar <[email protected]>

Reviewed-by: Nick Desaulniers <[email protected]>
(Sorry for the fallout from b059f801a937, but this is giving us a
pretty good idea about what "runtime" requirements certain configs
have. It would be cool to eventually have some kind of kexec test
case that folks could run in QEMU).

> ---
> arch/x86/purgatory/Makefile | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index 527749066d31..fb4ee5444379 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -25,6 +25,7 @@ KCOV_INSTRUMENT := n
>
> PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
> PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
> +PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN)
>
> # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
> # in turn leaves some undefined symbols like __fentry__ in purgatory and not
> --
> 2.21.0
>

--
Thanks,
~Nick Desaulniers

2019-09-25 17:02:38

by tip-bot2 for Alexey Makhalov

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Subject: [tip: x86/urgent] x86/purgatory: Disable the stackleak GCC plugin for the purgatory

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: ca14c996afe7228ff9b480cf225211cc17212688
Gitweb: https://git.kernel.org/tip/ca14c996afe7228ff9b480cf225211cc17212688
Author: Arvind Sankar <[email protected]>
AuthorDate: Mon, 23 Sep 2019 13:17:54 -04:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Mon, 23 Sep 2019 19:48:02 +02:00

x86/purgatory: Disable the stackleak GCC plugin for the purgatory

Since commit:

b059f801a937 ("x86/purgatory: Use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS")

kexec breaks if GCC_PLUGIN_STACKLEAK=y is enabled, as the purgatory
contains undefined references to stackleak_track_stack.

Attempting to load a kexec kernel results in this failure:

kexec: Undefined symbol: stackleak_track_stack
kexec-bzImage64: Loading purgatory failed

Fix this by disabling the stackleak plugin for the purgatory.

Signed-off-by: Arvind Sankar <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: b059f801a937 ("x86/purgatory: Use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS")
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/purgatory/Makefile | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 10fb42d..b81b517 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -23,6 +23,7 @@ KCOV_INSTRUMENT := n

PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
+PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN)

# Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
# in turn leaves some undefined symbols like __fentry__ in purgatory and not

2019-09-25 17:02:48

by tip-bot2 for Alexey Makhalov

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