[PATCH] um: make stub data pages size tweakable
Johannes Berg
johannes at sipsolutions.net
Fri Apr 14 06:46:39 PDT 2023
From: Johannes Berg <johannes.berg at intel.com>
There's a lot of code here that hard-codes that the
data is a single page, and right now that seems to
be sufficient, but to make it easier to change this
in the future, add a new STUB_DATA_PAGES constant
and use it throughout the code.
Signed-off-by: Johannes Berg <johannes.berg at intel.com>
---
Note the seccomp patchset contained something similar,
with a different rationale:
https://patchwork.ozlabs.org/project/linux-um/patch/20221122100759.208290-16-benjamin@sipsolutions.net/
However this is broken in a few places, e.g. 32-bit
and the lack of alignment, so we should probably do
this first correctly and then do seccomp again on top.
---
arch/um/include/shared/as-layout.h | 3 ++-
arch/um/kernel/skas/clone.c | 5 +++--
arch/um/kernel/skas/mmu.c | 6 +++---
arch/um/kernel/um_arch.c | 10 +++++++---
arch/um/os-Linux/skas/process.c | 6 +++---
arch/x86/um/shared/sysdep/stub_32.h | 8 ++++----
arch/x86/um/shared/sysdep/stub_64.h | 8 ++++----
arch/x86/um/stub_segv.c | 2 +-
8 files changed, 27 insertions(+), 21 deletions(-)
diff --git a/arch/um/include/shared/as-layout.h b/arch/um/include/shared/as-layout.h
index 9a0bd648d872..9ec3015bc5e2 100644
--- a/arch/um/include/shared/as-layout.h
+++ b/arch/um/include/shared/as-layout.h
@@ -23,7 +23,8 @@
#define STUB_START stub_start
#define STUB_CODE STUB_START
#define STUB_DATA (STUB_CODE + UM_KERN_PAGE_SIZE)
-#define STUB_END (STUB_DATA + UM_KERN_PAGE_SIZE)
+#define STUB_DATA_PAGES 1 /* must be a power of two */
+#define STUB_END (STUB_DATA + STUB_DATA_PAGES * UM_KERN_PAGE_SIZE)
#ifndef __ASSEMBLY__
diff --git a/arch/um/kernel/skas/clone.c b/arch/um/kernel/skas/clone.c
index ff5061f29167..62435187dda4 100644
--- a/arch/um/kernel/skas/clone.c
+++ b/arch/um/kernel/skas/clone.c
@@ -24,11 +24,12 @@
void __attribute__ ((__section__ (".__syscall_stub")))
stub_clone_handler(void)
{
- struct stub_data *data = get_stub_page();
+ struct stub_data *data = get_stub_data();
long err;
err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD,
- (unsigned long)data + UM_KERN_PAGE_SIZE / 2);
+ (unsigned long)data +
+ STUB_DATA_PAGES * UM_KERN_PAGE_SIZE / 2);
if (err) {
data->parent_err = err;
goto done;
diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index 125df465e8ea..656fe16c9b63 100644
--- a/arch/um/kernel/skas/mmu.c
+++ b/arch/um/kernel/skas/mmu.c
@@ -21,7 +21,7 @@ int init_new_context(struct task_struct *task, struct mm_struct *mm)
unsigned long stack = 0;
int ret = -ENOMEM;
- stack = get_zeroed_page(GFP_KERNEL);
+ stack = __get_free_pages(GFP_KERNEL | __GFP_ZERO, ilog2(STUB_DATA_PAGES));
if (stack == 0)
goto out;
@@ -52,7 +52,7 @@ int init_new_context(struct task_struct *task, struct mm_struct *mm)
out_free:
if (to_mm->id.stack != 0)
- free_page(to_mm->id.stack);
+ free_pages(to_mm->id.stack, ilog2(STUB_DATA_PAGES));
out:
return ret;
}
@@ -74,6 +74,6 @@ void destroy_context(struct mm_struct *mm)
}
os_kill_ptraced_process(mmu->id.u.pid, 1);
- free_page(mmu->id.stack);
+ free_pages(mmu->id.stack, ilog2(STUB_DATA_PAGES));
free_ldt(mmu);
}
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 8dcda617b8bf..0a23a98d4ca0 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -326,9 +326,13 @@ int __init linux_main(int argc, char **argv)
add_arg(DEFAULT_COMMAND_LINE_CONSOLE);
host_task_size = os_get_top_address();
- /* reserve two pages for the stubs */
- host_task_size -= 2 * PAGE_SIZE;
- stub_start = host_task_size;
+ /* reserve a few pages for the stubs (taking care of data alignment) */
+ /* align the data portion */
+ BUILD_BUG_ON(!is_power_of_2(STUB_DATA_PAGES));
+ stub_start = (host_task_size - 1) & ~(STUB_DATA_PAGES * PAGE_SIZE - 1);
+ /* another page for the code portion */
+ stub_start -= PAGE_SIZE;
+ host_task_size = stub_start;
/*
* TASK_SIZE needs to be PGDIR_SIZE aligned or else exit_mmap craps
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index 810e27c94c09..d46f62223b45 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -263,7 +263,7 @@ static int userspace_tramp(void *stack)
if (stack != NULL) {
fd = phys_mapping(uml_to_phys(stack), &offset);
addr = mmap((void *) STUB_DATA,
- UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
+ STUB_DATA_PAGES * UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
MAP_FIXED | MAP_SHARED, fd, offset);
if (addr == MAP_FAILED) {
printk(UM_KERN_ERR "mapping segfault stack at 0x%lx failed, errno = %d\n",
@@ -278,7 +278,7 @@ static int userspace_tramp(void *stack)
(unsigned long) stub_segv_handler -
(unsigned long) __syscall_stub_start;
- set_sigstack((void *) STUB_DATA, UM_KERN_PAGE_SIZE);
+ set_sigstack((void *) STUB_DATA, STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO;
sa.sa_sigaction = (void *) v;
@@ -518,7 +518,7 @@ static int __init init_thread_regs(void)
thread_regs[REGS_IP_INDEX] = STUB_CODE +
(unsigned long) stub_clone_handler -
(unsigned long) __syscall_stub_start;
- thread_regs[REGS_SP_INDEX] = STUB_DATA + UM_KERN_PAGE_SIZE -
+ thread_regs[REGS_SP_INDEX] = STUB_DATA + STUB_DATA_PAGES * UM_KERN_PAGE_SIZE -
sizeof(void *);
#ifdef __SIGNAL_FRAMESIZE
thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;
diff --git a/arch/x86/um/shared/sysdep/stub_32.h b/arch/x86/um/shared/sysdep/stub_32.h
index 4c6c2be0c899..38fa894b65d0 100644
--- a/arch/x86/um/shared/sysdep/stub_32.h
+++ b/arch/x86/um/shared/sysdep/stub_32.h
@@ -89,19 +89,19 @@ static inline void remap_stack_and_trap(void)
"addl %4,%%ebx ; movl %%eax, (%%ebx) ;"
"int $3"
: :
- "g" (~(UM_KERN_PAGE_SIZE - 1)),
+ "g" (~(STUB_DATA_PAGES * UM_KERN_PAGE_SIZE - 1)),
"g" (STUB_MMAP_NR),
"g" (UML_STUB_FIELD_FD),
"g" (UML_STUB_FIELD_OFFSET),
"g" (UML_STUB_FIELD_CHILD_ERR),
- "c" (UM_KERN_PAGE_SIZE),
+ "c" (STUB_DATA_PAGES * UM_KERN_PAGE_SIZE),
"d" (PROT_READ | PROT_WRITE),
"S" (MAP_FIXED | MAP_SHARED)
:
"memory");
}
-static __always_inline void *get_stub_page(void)
+static __always_inline void *get_stub_data(void)
{
unsigned long ret;
@@ -109,7 +109,7 @@ static __always_inline void *get_stub_page(void)
"movl %%esp,%0 ;"
"andl %1,%0"
: "=a" (ret)
- : "g" (~(UM_KERN_PAGE_SIZE - 1)));
+ : "g" (~(STUB_DATA_PAGES * UM_KERN_PAGE_SIZE - 1)));
return (void *)ret;
}
diff --git a/arch/x86/um/shared/sysdep/stub_64.h b/arch/x86/um/shared/sysdep/stub_64.h
index 92ea1670cf1c..2de1c8f88173 100644
--- a/arch/x86/um/shared/sysdep/stub_64.h
+++ b/arch/x86/um/shared/sysdep/stub_64.h
@@ -98,18 +98,18 @@ static inline void remap_stack_and_trap(void)
"int3"
: :
"g" (STUB_MMAP_NR),
- "g" (~(UM_KERN_PAGE_SIZE - 1)),
+ "g" (~(STUB_DATA_PAGES * UM_KERN_PAGE_SIZE - 1)),
"g" (MAP_FIXED | MAP_SHARED),
"g" (UML_STUB_FIELD_FD),
"g" (UML_STUB_FIELD_OFFSET),
"g" (UML_STUB_FIELD_CHILD_ERR),
- "S" (UM_KERN_PAGE_SIZE),
+ "S" (STUB_DATA_PAGES * UM_KERN_PAGE_SIZE),
"d" (PROT_READ | PROT_WRITE)
:
__syscall_clobber, "r10", "r8", "r9");
}
-static __always_inline void *get_stub_page(void)
+static __always_inline void *get_stub_data(void)
{
unsigned long ret;
@@ -117,7 +117,7 @@ static __always_inline void *get_stub_page(void)
"movq %%rsp,%0 ;"
"andq %1,%0"
: "=a" (ret)
- : "g" (~(UM_KERN_PAGE_SIZE - 1)));
+ : "g" (~(STUB_DATA_PAGES * UM_KERN_PAGE_SIZE - 1)));
return (void *)ret;
}
diff --git a/arch/x86/um/stub_segv.c b/arch/x86/um/stub_segv.c
index f7eefba034f9..040668b989b5 100644
--- a/arch/x86/um/stub_segv.c
+++ b/arch/x86/um/stub_segv.c
@@ -11,7 +11,7 @@
void __attribute__ ((__section__ (".__syscall_stub")))
stub_segv_handler(int sig, siginfo_t *info, void *p)
{
- struct faultinfo *f = get_stub_page();
+ struct faultinfo *f = get_stub_data();
ucontext_t *uc = p;
GET_FAULTINFO_FROM_MC(*f, &uc->uc_mcontext);
--
2.39.2
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