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Date: Tue, 29 Sep 2020 13:57:43 -0700
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: tglx@...utronix.de, mingo@...nel.org, bp@...e.de, luto@...nel.org,
x86@...nel.org
Cc: len.brown@...el.com, dave.hansen@...el.com, hjl.tools@...il.com,
Dave.Martin@....com, mpe@...erman.id.au, tony.luck@...el.com,
ravi.v.shankar@...el.com, libc-alpha@...rceware.org,
linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
linux-kernel@...r.kernel.org, chang.seok.bae@...el.com
Subject: [RFC PATCH 1/4] x86/signal: Introduce helpers to get the maximum signal frame size
Signal frames do not have a fixed format and can vary in size when a number
of things change: support XSAVE features, 32 vs. 64-bit apps. Add the code
to support a runtime method for userspace to dynamically discover how large
a signal stack needs to be.
Introduce a new variable, max_frame_size, and helper functions for the
calculation to be used in a new user interface. Set max_frame_size to a
system-wide worst-case value, instead of storing multiple app-specific
values.
Locate the body of the helper function -- fpu__get_fpstate_sigframe_size()
in fpu/signal.c for its relevance.
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Reviewed-by: Len Brown <len.brown@...el.com>
Cc: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
---
arch/x86/include/asm/fpu/signal.h | 2 ++
arch/x86/include/asm/sigframe.h | 23 ++++++++++++++++
arch/x86/kernel/cpu/common.c | 3 +++
arch/x86/kernel/fpu/signal.c | 20 ++++++++++++++
arch/x86/kernel/signal.c | 45 +++++++++++++++++++++++++++++++
5 files changed, 93 insertions(+)
diff --git a/arch/x86/include/asm/fpu/signal.h b/arch/x86/include/asm/fpu/signal.h
index 7fb516b6893a..5bfbf8f2e5a3 100644
--- a/arch/x86/include/asm/fpu/signal.h
+++ b/arch/x86/include/asm/fpu/signal.h
@@ -29,6 +29,8 @@ unsigned long
fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
unsigned long *buf_fx, unsigned long *size);
+unsigned long fpu__get_fpstate_sigframe_size(void);
+
extern void fpu__init_prepare_fx_sw_frame(void);
#endif /* _ASM_X86_FPU_SIGNAL_H */
diff --git a/arch/x86/include/asm/sigframe.h b/arch/x86/include/asm/sigframe.h
index 84eab2724875..ac77f3f90bc9 100644
--- a/arch/x86/include/asm/sigframe.h
+++ b/arch/x86/include/asm/sigframe.h
@@ -52,6 +52,15 @@ struct rt_sigframe_ia32 {
char retcode[8];
/* fp state follows here */
};
+
+#define SIZEOF_sigframe_ia32 sizeof(struct sigframe_ia32)
+#define SIZEOF_rt_sigframe_ia32 sizeof(struct rt_sigframe_ia32)
+
+#else
+
+#define SIZEOF_sigframe_ia32 0
+#define SIZEOF_rt_sigframe_ia32 0
+
#endif /* defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) */
#ifdef CONFIG_X86_64
@@ -81,8 +90,22 @@ struct rt_sigframe_x32 {
/* fp state follows here */
};
+#define SIZEOF_rt_sigframe_x32 sizeof(struct rt_sigframe_x32)
+
#endif /* CONFIG_X86_X32_ABI */
+#define SIZEOF_rt_sigframe sizeof(struct rt_sigframe)
+
+#else
+
+#define SIZEOF_rt_sigframe 0
+
#endif /* CONFIG_X86_64 */
+#ifndef SIZEOF_rt_sigframe_x32
+#define SIZEOF_rt_sigframe_x32 0
+#endif
+
+void __init init_sigframe_size(void);
+
#endif /* _ASM_X86_SIGFRAME_H */
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index c5d6f17d9b9d..d0363e15ec2e 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -57,6 +57,7 @@
#include <asm/intel-family.h>
#include <asm/cpu_device_id.h>
#include <asm/uv/uv.h>
+#include <asm/sigframe.h>
#include "cpu.h"
@@ -1276,6 +1277,8 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
fpu__init_system(c);
+ init_sigframe_size();
+
#ifdef CONFIG_X86_32
/*
* Regardless of whether PCID is enumerated, the SDM says
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index a4ec65317a7f..9f009525f551 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -507,6 +507,26 @@ fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
return sp;
}
+
+unsigned long fpu__get_fpstate_sigframe_size(void)
+{
+ unsigned long xstate_size = xstate_sigframe_size();
+ unsigned long fsave_header_size = 0;
+
+ /*
+ * This space is needed on (most) 32-bit kernels, or when a 32-bit
+ * app is running on a 64-bit kernel. To keep things simple, just
+ * assume the worst case and always include space for 'freg_state',
+ * even for 64-bit apps on 64-bit kernels. This wastes a bit of
+ * space, but keeps the code simple.
+ */
+ if ((IS_ENABLED(CONFIG_IA32_EMULATION) ||
+ IS_ENABLED(CONFIG_X86_32)) && use_fxsr())
+ fsave_header_size = sizeof(struct fregs_state);
+
+ return fsave_header_size + xstate_size;
+}
+
/*
* Prepare the SW reserved portion of the fxsave memory layout, indicating
* the presence of the extended state information in the memory layout
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index be0d7d4152ec..239a0b23a4b0 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -663,6 +663,51 @@ SYSCALL_DEFINE0(rt_sigreturn)
return 0;
}
+/*
+ * The FP state frame contains an XSAVE buffer which must be 64-byte aligned.
+ * If a signal frame starts at an unaligned address, extra space is required.
+ * This is the max alignment padding, conservatively.
+ */
+#define MAX_XSAVE_PADDING 63UL
+
+/*
+ * The frame data is composed of the following areas and laid out as:
+ *
+ * -------------------------
+ * | alignment padding |
+ * -------------------------
+ * | (f)xsave frame |
+ * -------------------------
+ * | fsave header |
+ * -------------------------
+ * | siginfo + ucontext |
+ * -------------------------
+ */
+
+/* max_frame_size tells userspace the worst case signal stack size. */
+static unsigned long __ro_after_init max_frame_size;
+
+void __init init_sigframe_size(void)
+{
+ /*
+ * Use the largest of possible structure formats. This might
+ * slightly oversize the frame for 64-bit apps.
+ */
+
+ if (IS_ENABLED(CONFIG_X86_32) ||
+ IS_ENABLED(CONFIG_IA32_EMULATION))
+ max_frame_size = max((unsigned long)SIZEOF_sigframe_ia32,
+ (unsigned long)SIZEOF_rt_sigframe_ia32);
+
+ if (IS_ENABLED(CONFIG_X86_X32_ABI))
+ max_frame_size = max(max_frame_size, (unsigned long)SIZEOF_rt_sigframe_x32);
+
+ if (IS_ENABLED(CONFIG_X86_64))
+ max_frame_size = max(max_frame_size, (unsigned long)SIZEOF_rt_sigframe);
+
+ max_frame_size += fpu__get_fpstate_sigframe_size() + MAX_XSAVE_PADDING;
+}
+
static inline int is_ia32_compat_frame(struct ksignal *ksig)
{
return IS_ENABLED(CONFIG_IA32_EMULATION) &&
--
2.17.1
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