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ANDROID: 16K: Only madvise padding from dynamic linker context

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Only preform padding advise from the execution context on bionic's
dynamic linker. This ensures that madvise() doesn't have unwanted
side effects.

Also rearrange the order of fail checks in madvise_vma_pad_pages()
in order of ascending cost.

Bug: 330117029
Bug: 327600007
Bug: 330767927
Bug: 328266487
Bug: 329803029
Change-Id: I3e05b8780c6eda78007f86b613f8c11dd18ac28f
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
This commit is contained in:
Kalesh Singh 2024-04-19 14:41:35 -07:00
parent 2ca5e076c9
commit 1657717c12
1 changed files with 65 additions and 10 deletions
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75
mm/pgsize_migration.c
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@ -16,6 +16,7 @@
#include <linux/jump_label.h>
#include <linux/kobject.h>
#include <linux/kstrtox.h>
#include <linux/sched/task_stack.h>
#include <linux/slab.h>
#include <linux/sysfs.h>
@ -134,6 +135,56 @@ static __always_inline bool str_has_suffix(const char *str, const char *suffix)
return !strncmp(str + str_len - suffix_len, suffix, suffix_len);
}
/*
* The dynamic linker, or interpreter, operates within the process context
* of the binary that necessitated dynamic linking.
*
* Consequently, process context identifiers; like PID, comm, ...; cannot
* be used to differentiate whether the execution context belongs to the
* dynamic linker or not.
*
* linker_ctx() deduces whether execution is currently in the dynamic linker's
* context by correlating the current userspace instruction pointer with the
* VMAs of the current task.
*
* Returns true if in linker context, otherwise false.
*
* Caller must hold mmap lock in read mode.
*/
static inline bool linker_ctx(void)
{
struct pt_regs *regs = task_pt_regs(current);
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
struct file *file;
if (!regs)
return false;
vma = find_vma(mm, instruction_pointer(regs));
/* Current execution context, the VMA must be present */
BUG_ON(!vma);
file = vma->vm_file;
if (!file)
return false;
if ((vma->vm_flags & VM_EXEC)) {
char buf[64];
const int bufsize = sizeof(buf);
char *path;
memset(buf, 0, bufsize);
path = d_path(&file->f_path, buf, bufsize);
if (!strcmp(path, "/system/bin/linker64"))
return true;
}
return false;
}
/*
* Saves the number of padding pages for an ELF segment mapping
* in vm_flags.
@ -146,6 +197,7 @@ static __always_inline bool str_has_suffix(const char *str, const char *suffix)
* 4) The number of the pages in the range does not exceed VM_TOTAL_PAD_PAGES.
* 5) The VMA is a regular file backed VMA (filemap_fault)
* 6) The file backing the VMA is a shared library (*.so)
* 7) The madvise was requested by bionic's dynamic linker.
*/
void madvise_vma_pad_pages(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
@ -155,18 +207,9 @@ void madvise_vma_pad_pages(struct vm_area_struct *vma,
if (!is_pgsize_migration_enabled())
return;
/* Only handle this for file backed VMAs */
if (!vma->vm_file || !vma->vm_ops || vma->vm_ops->fault != filemap_fault)
return;
/* Limit this to only shared libraries (*.so) */
if (!str_has_suffix(vma->vm_file->f_path.dentry->d_name.name, ".so"))
return;
/*
* If the madvise range is it at the end of the file save the number of
* pages in vm_flags (only need 4 bits are needed for 16kB aligned ELFs).
* pages in vm_flags (only need 4 bits are needed for up to 64kB aligned ELFs).
*/
if (start <= vma->vm_start || end != vma->vm_end)
return;
@ -176,6 +219,18 @@ void madvise_vma_pad_pages(struct vm_area_struct *vma,
if (!nr_pad_pages || nr_pad_pages > VM_TOTAL_PAD_PAGES)
return;
/* Only handle this for file backed VMAs */
if (!vma->vm_file || !vma->vm_ops || vma->vm_ops->fault != filemap_fault)
return;
/* Limit this to only shared libraries (*.so) */
if (!str_has_suffix(vma->vm_file->f_path.dentry->d_name.name, ".so"))
return;
/* Only bionic's dynamic linker needs to hint padding pages. */
if (!linker_ctx())
return;
vma_set_pad_pages(vma, nr_pad_pages);
}