[PATCH v6 04/18] perf/x86: Rename and move get_segment_base() and make it global

Steven Rostedt
2025-04-25T14:56:14Z

get_segment_base() will be used by the unwind_user code, so make it
global and rename it so it doesn't conflict with a KVM function of the
same name.

As the function is no longer specific to perf, move it to ptrace.c as that
seems to be a better location for a generic function like this.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
arch/x86/events/core.c | 44 ++++-------------------------------
arch/x86/include/asm/ptrace.h | 2 ++
arch/x86/kernel/ptrace.c | 38 ++++++++++++++++++++++++++++++
3 files changed, 45 insertions(+), 39 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 85eb0eb1b284..524a59d9c2c4 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -42,6 +42,7 @@
#include <asm/ldt.h>
#include <asm/unwind.h>
#include <asm/uprobes.h>
+#include <asm/ptrace.h>
#include <asm/ibt.h>

#include "perf_event.h"
@@ -2807,41 +2808,6 @@ valid_user_frame(const void __user *fp, unsigned long size)
return __access_ok(fp, size);
}

-static unsigned long get_segment_base(unsigned int segment)
-{
- struct desc_struct *desc;
- unsigned int idx = segment >> 3;
-
- if ((segment & SEGMENT_TI_MASK) == SEGMENT_LDT) {
-#ifdef CONFIG_MODIFY_LDT_SYSCALL
- struct ldt_struct *ldt;
-
- /*
- * If we're not in a valid context with a real (not just lazy)
- * user mm, then don't even try.
- */
- if (!nmi_uaccess_okay())
- return 0;
-
- /* IRQs are off, so this synchronizes with smp_store_release */
- ldt = smp_load_acquire(&current->mm->context.ldt);
- if (!ldt || idx >= ldt->nr_entries)
- return 0;
-
- desc = &ldt->entries[idx];
-#else
- return 0;
-#endif
- } else {
- if (idx >= GDT_ENTRIES)
- return 0;
-
- desc = raw_cpu_ptr(gdt_page.gdt) + idx;
- }
-
- return get_desc_base(desc);
-}
-
#ifdef CONFIG_UPROBES
/*
* Heuristic-based check if uprobe is installed at the function entry.
@@ -2898,8 +2864,8 @@ perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry_ctx *ent
if (user_64bit_mode(regs))
return 0;

- cs_base = get_segment_base(regs->cs);
- ss_base = get_segment_base(regs->ss);
+ cs_base = segment_base_address(regs->cs);
+ ss_base = segment_base_address(regs->ss);

fp = compat_ptr(ss_base + regs->bp);
pagefault_disable();
@@ -3018,11 +2984,11 @@ static unsigned long code_segment_base(struct pt_regs *regs)
return 0x10 * regs->cs;

if (user_mode(regs) && regs->cs != __USER_CS)
- return get_segment_base(regs->cs);
+ return segment_base_address(regs->cs);
#else
if (user_mode(regs) && !user_64bit_mode(regs) &&
regs->cs != __USER32_CS)
- return get_segment_base(regs->cs);
+ return segment_base_address(regs->cs);
#endif
return 0;
}
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 50f75467f73d..59357ec98e52 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -314,6 +314,8 @@ static __always_inline bool regs_irqs_disabled(struct pt_regs *regs)
return !(regs->flags & X86_EFLAGS_IF);
}

+unsigned long segment_base_address(unsigned int segment);
+
/* Query offset/name of register from its name/offset */
extern int regs_query_register_offset(const char *name);
extern const char *regs_query_register_name(unsigned int offset);
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 095f04bdabdc..81353a09701b 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -41,6 +41,7 @@
#include <asm/syscall.h>
#include <asm/fsgsbase.h>
#include <asm/io_bitmap.h>
+#include <asm/mmu_context.h>

#include "tls.h"

@@ -339,6 +340,43 @@ static int set_segment_reg(struct task_struct *task,

#endif /* CONFIG_X86_32 */

+unsigned long segment_base_address(unsigned int segment)
+{
+ struct desc_struct *desc;
+ unsigned int idx = segment >> 3;
+
+ lockdep_assert_irqs_disabled();
+
+ if ((segment & SEGMENT_TI_MASK) == SEGMENT_LDT) {
+#ifdef CONFIG_MODIFY_LDT_SYSCALL
+ struct ldt_struct *ldt;
+
+ /*
+ * If we're not in a valid context with a real (not just lazy)
+ * user mm, then don't even try.
+ */
+ if (!nmi_uaccess_okay())
+ return 0;
+
+ /* IRQs are off, so this synchronizes with smp_store_release */
+ ldt = smp_load_acquire(&current->mm->context.ldt);
+ if (!ldt || idx >= ldt->nr_entries)
+ return 0;
+
+ desc = &ldt->entries[idx];
+#else
+ return 0;
+#endif
+ } else {
+ if (idx >= GDT_ENTRIES)
+ return 0;
+
+ desc = raw_cpu_ptr(gdt_page.gdt) + idx;
+ }
+
+ return get_desc_base(desc);
+}
+
static unsigned long get_flags(struct task_struct *task)
{
unsigned long retval = task_pt_regs(task)->flags;
--
2.47.2