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objtool,x86: Fix uaccess PUSHF/POPF validation 

Commit ab234a260b ("x86/pv: Rework arch_local_irq_restore() to not
use popf") replaced "push %reg; popf" with something like: "test
$0x200, %reg; jz 1f; sti; 1:", which breaks the pushf/popf symmetry
that commit ea24213d80 ("objtool: Add UACCESS validation") relies
on.

The result is:

  drivers/gpu/drm/amd/amdgpu/si.o: warning: objtool: si_common_hw_init()+0xf36: PUSHF stack exhausted

Meanwhile, commit c9c324dc22 ("objtool: Support stack layout changes
in alternatives") makes that we can actually use stack-ops in
alternatives, which means we can revert 1ff865e343 ("x86,smap: Fix
smap_{save,restore}() alternatives").

That in turn means we can limit the PUSHF/POPF handling of
ea24213d80 to those instructions that are in alternatives.

Fixes: ab234a260b ("x86/pv: Rework arch_local_irq_restore() to not use popf")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/YEY4rIbQYa5fnnEp@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2021-03-08 15:46:04 +01:00
parent a38fd87484
commit ba08abca66
2 changed files with 7 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
arch/x86/include/asm/smap.h
View File

@ -58,9 +58,8 @@ static __always_inline unsigned long smap_save(void)
unsigned long flags;
asm volatile ("# smap_save\n\t"
ALTERNATIVE("jmp 1f", "", X86_FEATURE_SMAP)
"pushf; pop %0; " __ASM_CLAC "\n\t"
"1:"
ALTERNATIVE("", "pushf; pop %0; " __ASM_CLAC "\n\t",
X86_FEATURE_SMAP)
: "=rm" (flags) : : "memory", "cc");
return flags;
@ -69,9 +68,8 @@ static __always_inline unsigned long smap_save(void)
static __always_inline void smap_restore(unsigned long flags)
{
asm volatile ("# smap_restore\n\t"
ALTERNATIVE("jmp 1f", "", X86_FEATURE_SMAP)
"push %0; popf\n\t"
"1:"
ALTERNATIVE("", "push %0; popf\n\t",
X86_FEATURE_SMAP)
: : "g" (flags) : "memory", "cc");
}

3
tools/objtool/check.c
View File

@ -2442,6 +2442,9 @@ static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
if (update_cfi_state(insn, &state->cfi, op))
return 1;
if (!insn->alt_group)
continue;
if (op->dest.type == OP_DEST_PUSHF) {
if (!state->uaccess_stack) {
state->uaccess_stack = 1;