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authorH. Peter Anvin <hpa@linux.intel.com>2014-04-29 16:46:09 -0700
committerH. Peter Anvin <hpa@linux.intel.com>2014-04-30 14:14:28 -0700
commit3891a04aafd668686239349ea58f3314ea2af86b (patch)
treef1c3b49ceb091a875aaa6e99b6b4a91ea79dc2ec /arch/x86/mm
parentd1db0eea852497762cab43b905b879dfcd3b8987 (diff)
x86-64, espfix: Don't leak bits 31:16 of %esp returning to 16-bit stack
The IRET instruction, when returning to a 16-bit segment, only restores the bottom 16 bits of the user space stack pointer. This causes some 16-bit software to break, but it also leaks kernel state to user space. We have a software workaround for that ("espfix") for the 32-bit kernel, but it relies on a nonzero stack segment base which is not available in 64-bit mode. In checkin: b3b42ac2cbae x86-64, modify_ldt: Ban 16-bit segments on 64-bit kernels we "solved" this by forbidding 16-bit segments on 64-bit kernels, with the logic that 16-bit support is crippled on 64-bit kernels anyway (no V86 support), but it turns out that people are doing stuff like running old Win16 binaries under Wine and expect it to work. This works around this by creating percpu "ministacks", each of which is mapped 2^16 times 64K apart. When we detect that the return SS is on the LDT, we copy the IRET frame to the ministack and use the relevant alias to return to userspace. The ministacks are mapped readonly, so if IRET faults we promote #GP to #DF which is an IST vector and thus has its own stack; we then do the fixup in the #DF handler. (Making #GP an IST exception would make the msr_safe functions unsafe in NMI/MC context, and quite possibly have other effects.) Special thanks to: - Andy Lutomirski, for the suggestion of using very small stack slots and copy (as opposed to map) the IRET frame there, and for the suggestion to mark them readonly and let the fault promote to #DF. - Konrad Wilk for paravirt fixup and testing. - Borislav Petkov for testing help and useful comments. Reported-by: Brian Gerst <brgerst@gmail.com> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> Link: http://lkml.kernel.org/r/1398816946-3351-1-git-send-email-hpa@linux.intel.com Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Andrew Lutomriski <amluto@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Dirk Hohndel <dirk@hohndel.org> Cc: Arjan van de Ven <arjan.van.de.ven@intel.com> Cc: comex <comexk@gmail.com> Cc: Alexander van Heukelum <heukelum@fastmail.fm> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: <stable@vger.kernel.org> # consider after upstream merge
Diffstat (limited to 'arch/x86/mm')
-rw-r--r--arch/x86/mm/dump_pagetables.c44
1 files changed, 33 insertions, 11 deletions
diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 20621d753d5f..167ffcac16ed 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -30,12 +30,14 @@ struct pg_state {
unsigned long start_address;
unsigned long current_address;
const struct addr_marker *marker;
+ unsigned long lines;
bool to_dmesg;
};
struct addr_marker {
unsigned long start_address;
const char *name;
+ unsigned long max_lines;
};
/* indices for address_markers; keep sync'd w/ address_markers below */
@@ -46,6 +48,7 @@ enum address_markers_idx {
LOW_KERNEL_NR,
VMALLOC_START_NR,
VMEMMAP_START_NR,
+ ESPFIX_START_NR,
HIGH_KERNEL_NR,
MODULES_VADDR_NR,
MODULES_END_NR,
@@ -68,6 +71,7 @@ static struct addr_marker address_markers[] = {
{ PAGE_OFFSET, "Low Kernel Mapping" },
{ VMALLOC_START, "vmalloc() Area" },
{ VMEMMAP_START, "Vmemmap" },
+ { ESPFIX_BASE_ADDR, "ESPfix Area", 16 },
{ __START_KERNEL_map, "High Kernel Mapping" },
{ MODULES_VADDR, "Modules" },
{ MODULES_END, "End Modules" },
@@ -182,7 +186,7 @@ static void note_page(struct seq_file *m, struct pg_state *st,
pgprot_t new_prot, int level)
{
pgprotval_t prot, cur;
- static const char units[] = "KMGTPE";
+ static const char units[] = "BKMGTPE";
/*
* If we have a "break" in the series, we need to flush the state that
@@ -197,6 +201,7 @@ static void note_page(struct seq_file *m, struct pg_state *st,
st->current_prot = new_prot;
st->level = level;
st->marker = address_markers;
+ st->lines = 0;
pt_dump_seq_printf(m, st->to_dmesg, "---[ %s ]---\n",
st->marker->name);
} else if (prot != cur || level != st->level ||
@@ -208,17 +213,24 @@ static void note_page(struct seq_file *m, struct pg_state *st,
/*
* Now print the actual finished series
*/
- pt_dump_seq_printf(m, st->to_dmesg, "0x%0*lx-0x%0*lx ",
- width, st->start_address,
- width, st->current_address);
-
- delta = (st->current_address - st->start_address) >> 10;
- while (!(delta & 1023) && unit[1]) {
- delta >>= 10;
- unit++;
+ if (!st->marker->max_lines ||
+ st->lines < st->marker->max_lines) {
+ pt_dump_seq_printf(m, st->to_dmesg,
+ "0x%0*lx-0x%0*lx ",
+ width, st->start_address,
+ width, st->current_address);
+
+ delta = st->current_address - st->start_address;
+ while (!(delta & 1023) && unit[1]) {
+ delta >>= 10;
+ unit++;
+ }
+ pt_dump_cont_printf(m, st->to_dmesg, "%9lu%c ",
+ delta, *unit);
+ printk_prot(m, st->current_prot, st->level,
+ st->to_dmesg);
}
- pt_dump_cont_printf(m, st->to_dmesg, "%9lu%c ", delta, *unit);
- printk_prot(m, st->current_prot, st->level, st->to_dmesg);
+ st->lines++;
/*
* We print markers for special areas of address space,
@@ -226,7 +238,17 @@ static void note_page(struct seq_file *m, struct pg_state *st,
* This helps in the interpretation.
*/
if (st->current_address >= st->marker[1].start_address) {
+ if (st->marker->max_lines &&
+ st->lines > st->marker->max_lines) {
+ unsigned long nskip =
+ st->lines - st->marker->max_lines;
+ pt_dump_seq_printf(m, st->to_dmesg,
+ "... %lu entr%s skipped ... \n",
+ nskip,
+ nskip == 1 ? "y" : "ies");
+ }
st->marker++;
+ st->lines = 0;
pt_dump_seq_printf(m, st->to_dmesg, "---[ %s ]---\n",
st->marker->name);
}