diff options
| author | Benjamin Berg <benjamin.berg@intel.com> | 2024-09-19 14:45:07 +0200 |
|---|---|---|
| committer | Johannes Berg <johannes.berg@intel.com> | 2024-10-10 13:37:22 +0200 |
| commit | 91f0a0c5cc5bc863888a936fbd05394c6e284466 (patch) | |
| tree | 6b42aa2932bf01d303eae08fafc4ce785c74f791 /arch/x86 | |
| parent | um: Add compile time assert that stub fits on a page (diff) | |
| download | linux-91f0a0c5cc5bc863888a936fbd05394c6e284466.tar.xz linux-91f0a0c5cc5bc863888a936fbd05394c6e284466.zip | |
um: Calculate stub data address relative to stub code
Instead of using the current stack pointer, we can also use the current
instruction to calculate where the stub data is. With this the stub data
only needs to be aligned to a full page boundary.
Changing this has the advantage that we do not have a hole in the memory
space above the stub data (which would need to be explicitly cleared).
Another motivation to do this is that with the planned addition of a
SECCOMP based userspace the stack pointer may not be fully trustworthy.
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20240919124511.282088-7-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/um/shared/sysdep/stub_32.h | 10 | ||||
| -rw-r--r-- | arch/x86/um/shared/sysdep/stub_64.h | 8 |
2 files changed, 12 insertions, 6 deletions
diff --git a/arch/x86/um/shared/sysdep/stub_32.h b/arch/x86/um/shared/sysdep/stub_32.h index 0b44a86dd346..631a18d0ff44 100644 --- a/arch/x86/um/shared/sysdep/stub_32.h +++ b/arch/x86/um/shared/sysdep/stub_32.h @@ -112,10 +112,14 @@ static __always_inline void *get_stub_data(void) unsigned long ret; asm volatile ( - "movl %%esp,%0 ;" - "andl %1,%0" + "call _here_%=;" + "_here_%=:" + "popl %0;" + "andl %1, %0 ;" + "addl %2, %0 ;" : "=a" (ret) - : "g" (~(STUB_DATA_PAGES * UM_KERN_PAGE_SIZE - 1))); + : "g" (~(UM_KERN_PAGE_SIZE - 1)), + "g" (UM_KERN_PAGE_SIZE)); return (void *)ret; } diff --git a/arch/x86/um/shared/sysdep/stub_64.h b/arch/x86/um/shared/sysdep/stub_64.h index 8e4ff39dcade..17153dfd780a 100644 --- a/arch/x86/um/shared/sysdep/stub_64.h +++ b/arch/x86/um/shared/sysdep/stub_64.h @@ -117,10 +117,12 @@ static __always_inline void *get_stub_data(void) unsigned long ret; asm volatile ( - "movq %%rsp,%0 ;" - "andq %1,%0" + "lea 0(%%rip), %0;" + "andq %1, %0 ;" + "addq %2, %0 ;" : "=a" (ret) - : "g" (~(STUB_DATA_PAGES * UM_KERN_PAGE_SIZE - 1))); + : "g" (~(UM_KERN_PAGE_SIZE - 1)), + "g" (UM_KERN_PAGE_SIZE)); return (void *)ret; } |