Commit-ID: 7fcb3bc361c724a75bc642dbdd9d9bf0bdf07260 Gitweb: http://git.kernel.org/tip/7fcb3bc361c724a75bc642dbdd9d9bf0bdf07260 Author: Ingo Molnar <mingo@xxxxxxxxxx> AuthorDate: Tue, 17 Mar 2015 14:42:59 +0100 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Tue, 17 Mar 2015 16:01:41 +0100 x86/asm/entry/64: Update comments about stack frames Tweak a few outdated comments that were obsoleted by recent changes to syscall entry code: - we no longer have a "partial stack frame" on entry, ever. - explain the syscall entry usage of old_rsp. Partially based on a (split out of) patch from Denys Vlasenko. Originally-from: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Acked-by: Borislav Petkov <bp@xxxxxxxxx> Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: Will Drewry <wad@xxxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- arch/x86/kernel/entry_64.S | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index aed3f11..d287f78 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -15,10 +15,8 @@ * after an interrupt and after each system call. * * A note on terminology: - * - top of stack: Architecture defined interrupt frame from SS to RIP + * - iret frame: Architecture defined interrupt frame from SS to RIP * at the top of the kernel process stack. - * - partial stack frame: partially saved registers up to R11. - * - full stack frame: Like partial stack frame, but all register saved. * * Some macro usage: * - CFI macros are used to generate dwarf2 unwind information for better @@ -219,7 +217,7 @@ ENDPROC(native_usergs_sysret64) * Interrupts are off on entry. * Only called from user space. * - * When user can change the frames always force IRET. That is because + * When user can change pt_regs->foo always force IRET. That is because * it deals with uncanonical addresses better. SYSRET has trouble * with them due to bugs in both AMD and Intel CPUs. */ @@ -238,6 +236,11 @@ ENTRY(system_call) */ GLOBAL(system_call_after_swapgs) + /* + * We use 'old_rsp' as a scratch register, hence this block must execute + * atomically in the face of possible interrupt-driven task preemption, + * so we can enable interrupts only after we're done with using old_rsp: + */ movq %rsp,PER_CPU_VAR(old_rsp) /* kernel_stack is set so that 5 slots (iret frame) are preallocated */ movq PER_CPU_VAR(kernel_stack),%rsp @@ -303,7 +306,7 @@ int_ret_from_sys_call_fixup: FIXUP_TOP_OF_STACK %r11 jmp int_ret_from_sys_call - /* Do syscall tracing */ + /* Do syscall entry tracing */ tracesys: movq %rsp, %rdi movq $AUDIT_ARCH_X86_64, %rsi @@ -339,11 +342,11 @@ tracesys_phase2: movq %r10,%rcx /* fixup for C */ call *sys_call_table(,%rax,8) movq %rax,RAX(%rsp) - /* Use IRET because user could have changed frame */ + /* Use IRET because user could have changed pt_regs->foo */ /* * Syscall return path ending with IRET. - * Has correct top of stack, but partial stack frame. + * Has correct iret frame. */ GLOBAL(int_ret_from_sys_call) DISABLE_INTERRUPTS(CLBR_NONE) @@ -374,7 +377,7 @@ int_careful: TRACE_IRQS_OFF jmp int_with_check - /* handle signals and tracing -- both require a full stack frame */ + /* handle signals and tracing -- both require a full pt_regs */ int_very_careful: TRACE_IRQS_ON ENABLE_INTERRUPTS(CLBR_NONE) -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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