diff options
| author | Johannes Berg <johannes.berg@intel.com> | 2024-10-22 14:02:38 +0200 |
|---|---|---|
| committer | Johannes Berg <johannes.berg@intel.com> | 2024-10-23 09:04:59 +0200 |
| commit | 14d4a7b516e993cf3926758a7ede569d8e119855 (patch) | |
| tree | 73944a9852888a5207123438899c8aa684d39a0b | |
| parent | 8508a5e0e9db3932ca43651f86ba1042a1e9f4ca (diff) | |
um: make stub_exe _start() pure inline asm
Since __attribute__((naked)) cannot be used with functions
containing C statements, just generate the few instructions
it needs in assembly directly.
While at it, fix the stack usage ("1 + 2*x - 1" is odd) and
document what it must do, and why it must adjust the stack.
Fixes: 8508a5e0e9db ("um: Fix misaligned stack in stub_exe")
Link: https://lore.kernel.org/linux-um/CABVgOSntH-uoOFMP5HwMXjx_f1osMnVdhgKRKm4uz6DFm2Lb8Q@mail.gmail.com/
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
| -rw-r--r-- | arch/um/kernel/skas/stub_exe.c | 18 | ||||
| -rw-r--r-- | arch/x86/um/shared/sysdep/stub_32.h | 8 | ||||
| -rw-r--r-- | arch/x86/um/shared/sysdep/stub_64.h | 8 |
3 files changed, 27 insertions, 7 deletions
diff --git a/arch/um/kernel/skas/stub_exe.c b/arch/um/kernel/skas/stub_exe.c index 722ce6267476..23c99b285e82 100644 --- a/arch/um/kernel/skas/stub_exe.c +++ b/arch/um/kernel/skas/stub_exe.c @@ -81,11 +81,15 @@ noinline static void real_init(void) __attribute__((naked)) void _start(void) { - char *alloc; - - /* Make enough space for the stub (including space for alignment) */ - alloc = __builtin_alloca((1 + 2 * STUB_DATA_PAGES - 1) * UM_KERN_PAGE_SIZE); - asm volatile("" : "+r,m"(alloc) : : "memory"); - - real_init(); + /* + * Since the stack after exec() starts at the top-most address, + * but that's exactly where we also want to map the stub data + * and code, this must: + * - push the stack by 1 code and STUB_DATA_PAGES data pages + * - call real_init() + * This way, real_init() can use the stack normally, while the + * original stack further down (higher address) will become + * inaccessible after the mmap() calls above. + */ + stub_start(real_init); } diff --git a/arch/x86/um/shared/sysdep/stub_32.h b/arch/x86/um/shared/sysdep/stub_32.h index 631a18d0ff44..390988132c0a 100644 --- a/arch/x86/um/shared/sysdep/stub_32.h +++ b/arch/x86/um/shared/sysdep/stub_32.h @@ -123,4 +123,12 @@ static __always_inline void *get_stub_data(void) return (void *)ret; } + +#define stub_start(fn) \ + asm volatile ( \ + "subl %0,%%esp ;" \ + "movl %1, %%eax ; " \ + "call *%%eax ;" \ + :: "i" ((1 + STUB_DATA_PAGES) * UM_KERN_PAGE_SIZE), \ + "i" (&fn)) #endif diff --git a/arch/x86/um/shared/sysdep/stub_64.h b/arch/x86/um/shared/sysdep/stub_64.h index 17153dfd780a..294affbec742 100644 --- a/arch/x86/um/shared/sysdep/stub_64.h +++ b/arch/x86/um/shared/sysdep/stub_64.h @@ -126,4 +126,12 @@ static __always_inline void *get_stub_data(void) return (void *)ret; } + +#define stub_start(fn) \ + asm volatile ( \ + "subq %0,%%rsp ;" \ + "movq %1,%%rax ;" \ + "call *%%rax ;" \ + :: "i" ((1 + STUB_DATA_PAGES) * UM_KERN_PAGE_SIZE), \ + "i" (&fn)) #endif |